Car Rattles When Accelerating: 9 Causes

Are you hearing a metal rattling noise from the engine bay or front end of your car when you hit the gas pedal? Do you feel vibrations from the engine when you press the accelerator? Car rattles when accelerating can be a concerning issue for a car owner. It not only disrupts the driving experience but can also indicate a problem with the car.

Who wouldn’t want to get rid of that annoying rattle when accelerating uphill or on a flat road, and get their car running smoothly again? Trust me, I know I would. And I bet you would too. In this blog post, we’ll go over the most common causes of car rattles when accelerating, and what you can do to fix them.

The most common cause of car rattles when accelerating is a loose heat shield of the catalytic converter/exhaust system. Heat shields can become loose or detached, they can cause a rattling sound when your car accelerates. Another common cause of a metal rattling sound in the car when accelerating is a loose exhaust system. The exhaust system of your car is made up of several components all held together with a series of bolts and clamps. If these bolts or clamps become loose, it can cause the exhaust components to start to vibrate and rattle against each other. Another potential cause of a car rattling when accelerating is an overly worn engine mount. Engine mounts are what keep the engine firmly in place, and if they become overly worn they can cause the engine to move around and vibrate, creating a rattle when the engine is revved. Car rattles when accelerating can also be caused by a worn-out suspension system. If your suspension is worn out, it can cause your car to vibrate and create a rattling sound. Low oil levels can also cause a rattle noise when accelerating as it can damage the cam phaser and hydraulic valve lifter. Finally, it is possible that the rattle could be coming from something else entirely. It could be a loose belt, a bad pulley, an exhaust leak, or even a worn spark plug.

Causes Of Car Makes Rattle Noise When Accelerating

1. Bad or Low Transmission Fluid

Low or bad transmission fluid can cause a variety of issues, including the dreaded rattle noise when accelerating.

Transmission fluid is a special lubricant designed specifically for the smooth operation of the automatic transmission system of your vehicle. It provides hydraulic power to engage and disengage the torque converter. Moreover, transmission oil also passes through solenoid valves in the valve body of the automatic transmission to engage and disengage gears. Moreover, transmission fluid also lubricates gears in the drivetrain.

When transmission fluid becomes bad, it will cause rattling and grinding noises in transmission as gears will shift hard due to the poor quality of transmission oil.

The most common cause of low transmission fluid is a leak. Leaks can occur in the transmission pan, seals, and gaskets, as well as in the lines that connect the transmission to the engine. If left unchecked, the leak can eventually cause the transmission to run dry, resulting in a rattling noise when accelerating.

Another common cause of a bad quality transmission fluid is a clogged transmission filter. The transmission filter is responsible for removing dirt and debris from the fluid, and when it fails, debris can clog the lines, leading to a decrease in fluid flow. This can cause the transmission to make a rattle noise when accelerating.

How to spot the cause?

You should first check the level of transmission fluid. To check transmission fluid, you’ll find a dipstick under the hood. You would not want to confuse the transmission fluid dipstick with the engine oil dipstick. Both are different. Moreover, you should start the engine and warm it up to its operating temperature before measuring the level of transmission fluid.

If the level of transmission fluid is fine, you should check the quality of transmission fluid by wiping the transmission oil dipstick with a clean white cloth. If the color of the transmission fluid has no reddish tint, you should change the transmission fluid. I have written a detailed guide on transmission flush to learn more.

2. Low Oil Level

When it comes to the engine and its operations, one of the most crucial and important components is the lubrication system. Without it, all of the metal parts inside an engine will grind and wear down very quickly, resulting in a broken-down vehicle. Low engine oil levels are one of the most common causes of car making rattle noise when accelerating, and it can cause a multitude of issues from minor to major.

The most common issue caused by low engine oil levels is damage to cam phasers, hydraulic lifters, and rod bearings.

Cam phasers are located in the engine and help regulate the timing of the engine’s valves. They are designed to adjust the timing of the valves in order to increase performance and fuel economy. When the engine oil level is low, the cam phasers can become misaligned, resulting in a rattle noise when the car is accelerating.

The hydraulic lifters, also known as hydraulic valve lifters, are responsible for lifting the valves off their seats when the engine is running. This allows for better fuel and airflow through the cylinder. When the engine oil level is low, hydraulic valve lifters do not operate properly and can cause a rattling sound.

Connecting Rod bearings are also put under a lot of strain at low oil levels, and they can start to wear out faster than normal. This will result in the engine making a metal rattling noise when accelerating.

How to spot the cause?

Low oil in the engine can also turn on the low oil level light on the dashboard. So, you should first check the oil level from the oil dipstick.

If your engine is burning oil, the oil must be leaking from somewhere. In that case, you should check the coolant color. If it has coffee-like color, it means that oil is leaking into the engine. In that case, you should especially check the engine head gasket.

There are also other spots of oil leakage in the engine. These include:

• Oil Pan Gasket
• Oil Filter
• Oil Pan Drain Plug
• Valve Cover Gasket 
• Oil Pressure Sending Unit (you can find its location in your vehicle’s owner’s manual)

You can read my guide on common oil leaks in engines to learn more. Moreover, when changing motor oil, make sure that you’re using the correct viscosity grade. For this, I’ve written a guide on 10w30 vs SAE 30 to learn more.

3. Rattling Heat Shield

Heat shields are metal panels that are designed to protect other components, such as your exhaust system, from the heat generated by your engine.

When the heat shield is loose, or the bolts that hold it in place become loose, it can start to rattle. The vibration from the engine can cause the heat shield to vibrate, and this vibration can be heard as a rattling sound when you accelerate.

There are several reasons why a heat shield can start to rattle. The most common cause is rust and corrosion. Over time, the shield can become corroded due to exposure to the elements and road salts. This can cause the shield to become loose and start to rattle.

Another cause of rattling heat shields is the loose mounting hardware. Heat shields are usually held in place by bolts, nuts, and brackets. If these become loose, the shield can start to vibrate and produce a rattling sound.

How to spot the cause?

Spotting the source of a rattle caused by a heat shield can be a relatively straightforward job if you follow the right steps. To begin with, make sure you wear some protective gloves, preferably leather gloves, which provide some insulation from the heat generated by the engine. 

Next, you need to start the engine and let it idle for a few minutes in order to allow it to warm up. This is important because it will help you find the cause of the rattling more quickly and accurately. As the engine is running, you should carefully observe the area around the heat shields and keep an eye out for any moving parts. 

Once you have identified the potential source of the rattling, it is time to apply some gentle pressure to the heat shields to see if it stops the noise. You can do this with your hands or using a stick or a screwdriver. You should make sure to apply the pressure gradually and evenly, so as not to damage the heat shields. If the rattling stops when the pressure is applied, then the heat shield is most likely the culprit.

How to fix?

You can use a hose clamp to fix the heat shield rattle in the car. You can also try tightening the screws and bolts of the heat shield to fix the rattle.

One person faced the car rattling issue due to a loose heat shield. He simply fixed it with a worm clamp as you can see in the picture below:

4. Loose Exhaust System

One possible cause of a rattling sound when accelerating is a loose exhaust system. The exhaust system includes the muffler, catalytic converter, and exhaust pipes. If any of these components are loose, they may shake and cause a rattling noise. 

Below are the most common causes of a rattling exhaust sound when accelerating:

1. Loose Muffler: The muffler is the part of the exhaust system that reduces noise. It’s usually made of thick metal and fastened securely to the exhaust pipes. If the muffler is loose, it will vibrate and create a rattling sound.
2. Damaged Exhaust System: If the exhaust system has any holes or cracks, it will allow air to escape and make a rattling sound when accelerating.

How to fix?
Here are some tips for fixing a loose exhaust system:

• Tighten the bolts and clamps: The first step is to check all of the bolts and clamps that connect the exhaust components. Make sure that they are all tightly secured.
• Inspect the hangers: The exhaust components are held in place by hangers. These can become worn and stretched over time. In that case, you should check the hangers and replace any that are worn.
• Check for corrosion: Exhaust components can also become corroded over time. So, inspect for any signs of corrosion and replace any components that are corroded.

5. Bad Catalytic Converter

When a catalytic converter is damaged, it can cause your car to make a rattle noise when you accelerate. This is because the ceramic honeycomb inside the catalytic converter can become dislodged, causing it to vibrate against the walls of the converter. 

How to spot the issue?

To determine whether a rattling noise is caused by a catalytic converter, you can bang the hammer or mallet a couple of times. If you hear the rattle then the problem is solved. You can also remove the catalytic converter and see if any ceramic falls out.

If a catalytic converter goes bad, it can also throw the P0420 code. You can check it with the OBD2 reader.

6. Bad Strut Mounts

If the rattling noise is coming from the front of your car, the chances are that strut mounts have gone bad.

Strut mounts are an important component of your car’s suspension system. They attach the suspension strut to the vehicle and help to absorb the shocks and vibrations from the road. They’re made from rubber and metal and are designed to be durable and long-lasting.

When your strut mounts are in good condition, they allow for a smooth ride and help to reduce noise and vibration from the road. But when they start to wear out, they can cause a rattle noise when accelerating. The reason for this is that the worn strut mounts no longer offer the same level of shock absorption. As you accelerate, the tires hit bumps and imperfections in the road. The lack of shock absorption causes the suspension strut to move, which in turn causes the rattle noise.

How to spot?

There are a few signs that can indicate your strut mounts are bad. They include:

• Unusual noises when accelerating or driving over bumps.
• Loose or worn suspension components.
• Uneven tire wear.
• Sagging suspension.

7. Cracked Bushing Of Sway Bar

In many cases, the rattling noise you hear when you accelerate could be caused by a cracked or worn bushing of the sway bar. This part of the car’s suspension system helps to reduce body roll and make the car more stable.

These bushings are usually made of rubber or polyurethane and act as a fulcrum for the sway bar. They help to reduce vibration by absorbing and dissipating energy.

If the sway bar bushings become cracked or worn, they can become loose and start to make noise when you drive. This is because the sway bar is no longer tightly connected to the frame, so it rattles around every time you hit a bump.

Thus, if you’re hearing a rattling sound when you accelerate, it’s worth checking out your sway bar bushings to see if they need to be replaced.

The most recommended bushing for a sway bar is Moog Stabilizer Bar Bushing.

8. Loose or Bad Motor Mounts

Loose motor mounts can cause a car to make a rattling noise when accelerating. Motor mounts are an important part of any car’s engine and transmission system. These mounts are usually made of rubber or steel and are designed to reduce vibration and keep the engine and transmission in place. 

When motor mounts become loose over time, they can cause the engine and transmission to shift, resulting in a rattling noise when the car accelerates. This is because the mounts are no longer able to secure the engine and transmission in place. As the engine and transmission move, they make contact with other components, creating a rattling noise. 

How to spot?

To spot bad motor mounts, look at the motor mount to see if there are any visible signs of wear and tear. Check to see if the mount has any cracks or tears in the rubber or metal parts. 

6. Bad CV Joints

If you have a forward wheel drive vehicle, bad CV joints can cause a rattling or ticking noises in the front end of the engine.

CV joints are used to connect the drive shaft to the transmission, and their purpose is to transfer power from the engine to the wheels. When they become worn or damaged, they can cause rattling noises and other issues with your car’s performance. 

The CV joints are usually made of rubber that encloses grease and ball bearings. They can become worn over time due to friction, wear, and tear. As the wheels turn, the CV joints allow the drive axle to move up and down without binding or becoming stuck. This allows the wheels to maintain their contact with the ground, even when the vehicle is turning or accelerating. 

The most common cause of a bad CV joint is a lack of lubrication. Over time, the lubricant that is used to keep the joint lubricated can become dry, making it harder for the joint to move freely. This can cause the joint to wear out, resulting in a rattling noise when accelerating. 

How to spot?

If you’re observing grease stains underneath your vehicle, the chances are that the rubber boot of the CV joints is cracked.

7. Engine Knocking

Engine knocking, also known as pinging or detonation, is a common problem in cars that can cause a rattling noise in the engine bay. It is most often heard when the car is accelerating and is caused by the engine not running at the correct air-fuel ratio. When the air-fuel ratio is off, the fuel is not completely burned, causing an explosion in the cylinder that leads to the rattling noise. 

How to spot the cause?

Engine knocking can be caused by a variety of factors. Some of the most common causes include:

1. Bad Spark Plugs: Spark plugs are responsible for igniting the air-fuel mixture in the engine. If the spark plugs are worn out or damaged, they may not be able to ignite the mixture properly, resulting in engine knocking.
2. Bad Fuel Pressure Regulator: The fuel pressure regulator is responsible for keeping the fuel pressure in the engine constant. If the fuel pressure regulator is faulty, the fuel pressure can drop, resulting in incomplete combustion and engine knocking.
3. Bad Fuel Injectors: Fuel injectors are responsible for spraying fuel into the engine. If the fuel injectors are faulty or clogged, they may not be able to spray fuel into the engine properly, resulting in engine knocking.

Moreover, incomplete combustion can also throw engine misfire trouble codes. You can use this OBD2 tool to check codes.

8. Worn-out Serpentine Belt Pulleys

The serpentine belt is a common component found in the engine of most modern vehicles. It’s a long belt that wraps around several pulleys in your engine, including the idler pulley, tensioner pulley, and several other pulleys. The job of the serpentine belt is to power the components in your vehicle’s engine, such as the power steering pump, air conditioning compressor, and alternator.

When the serpentine belt pulleys become worn out, they can cause a rattling noise when you accelerate. This is because the worn-out pulleys can no longer keep the serpentine belt tight. When the belt is not tight, it can move around and cause the rattling sound.

How to spot?

The idler pulley should be tight. If idler pulley has any play, it will cause serpentine belt to become loose. Also, check if serpentine belt has any signs of wear.

9. Dust Shield Is Touching The Disc

A dust shield is a component of the car’s brakes that is designed to keep dust and other debris away from the brake discs and other components. It is typically made of metal or plastic and is attached to the car’s wheel assembly. 

When the dust shield is too close to the brake disc, it can cause a rattling noise in the front of the car when the car is accelerating. This occurs because the dust shield is vibrating against the brake disc and creating a rattling sound. This is usually caused by the dust shield being bent or misaligned, causing it to rub against the brake disc when it rotates.