Why Your Car Is Making a Rattling Noise When Driving Slow

Nobody likes hearing weird noises coming from their vehicles. You want a silent, hassle-free ride from your daily driver and a clean, revving sound from your special-occasions vehicle. Car owners dread unusual motor sounds because they often lead to trips to the mechanic.

Cars make rattling noises when driving slowly due to worn-out exhaust and engine components, leaking engine fluids, and loose exterior and interior connections. Solutions include the replacement of worn-out components and the fastening of loose components.

This article will explain the common causes of car rattling noises and how best to deal with them.

Reasons Your Car Is Making Rattling Noises at Low Speeds

There are three main reasons that your car might be making noise when it’s moving at low speeds:

  1. Worn-out exhaust and engine components
  2. Leaking engine fluids
  3. Loose exterior and interior components

I will discuss each of these potential culprits in detail in the following sections. Read on to learn more about the causes of a rattling sound in your car.

1. Worn-Out Exhaust and Engine Components

Diagnosing car rattling noises begins with identifying the source of the noise. If the source is near the back of the car, it’s likely an exhaust fault. If it’s under the hood, it’s probably an engine problem.

These are a few of the mechanical components that may be the source of the problem:

  • Worn exhaust mounts
  • Corroded heat shield
  • Worn catalytic converter
  • Worn piston and cylinder

Pay attention to your car’s functioning and examine each of these components to find the source of any rattling sounds.

Worn Exhaust Mounts

The exhaust system on your car undergoes a lot of stress, primarily due to the heat and corrosiveness of exhaust fumes. Furthermore, its placement under the car’s floor exposes it to dirt, grime, road salt, rock pebbles, snow, and forceful impacts.

As a result, the exhaust system deteriorates faster than other parts of the vehicle. One of the first parts to give in are the exhaust mounts.

Exhaust mounts support the exhaust under the car, reducing vibration between components.

As they wear down, their ability to prevent noise and vibration decreases. A rattling noise from the back of your vehicle often signifies worn exhaust mounts.

Replacement of the worn exhaust mounts will remedy this issue. Fortunately, exhaust mounts are not expensive, and you can buy new ones of durable construction.

Worn exhaust mounts aren’t a terminal issue, and you can drive with them for as long as you can bear the noise. However, I haven’t met many drivers that can comfortably deal with the rattle caused by worn exhaust mounts.

Corroded Heat Shield

Your car’s heat shield protects vulnerable car components from the heat produced by exhaust gasses. Heat shields are made from robust materials, meaning they don’t fail a lot.

Nevertheless, the rattling you hear might indicate heat shield failure.

How to Identify Heat Shield Corrosion

Identifying rattling caused by heat shield failure is relatively easy. If the area around the engine bay starts getting too hot when the rattling begins, the heat shield is the probable culprit.

Heat increases because of the shield’s compromised ability to contain heat produced during combustion. At times, the engine bay’s heat rises so high that it becomes difficult to open the hood.

You may also notice a burning smell in the engine bay, likely emanating from a plastic component disintegrating due to the excess heat. Rattling from a damaged heat shield is mostly audible during low speeds and may change in tone or intensity as speed increases.

An inspection of the heat shield determines the best way to deal with the noise. A corroded heat shield needs replacement, and a loose one requires proper fastening.

Worn Catalytic Converter

Catalytic converters lessen the impact of exhaust gasses on the environment by reducing them to less-harmful gasses. For instance, the converter converts carbon monoxide to carbon dioxide and water.

The catalytic converter houses catalysts arranged in a honeycomb pattern to increase the surface area in contact with the harmful gasses. It’s a bulbous section of the exhaust near the tip.

A failure of the honeycomb often manifests as a rattling noise coming from the catalytic converter. It’s commonly caused by degradation and sometimes by a direct impact on the converter.

Identifying a Worn Catalytic Converter

Rattling from the catalytic converter is often heard at low speeds before it catches temperature. However, it’s a straightforward failure to diagnose.

You’ll notice dark-colored, foul-smelling smoke coming from the exhaust and probably see the check engine warning light up. Furthermore, your car will struggle to maintain optimum performance levels.

Replacing your catalytic converter is the most efficient and time-effective solution to the problem. Catalytic converters can be expensive, but replacement provides a one-time fix to the issue.

Worn Engine Mounts and Bolts

Combustion produces a lot of energy that can lead to the loosening of engine mounts and bolts.

Engine mounts hold the transmission and engine in place. Most cars have two to three mounts holding the motor and another holding the transmission.

Identifying Rattling in Engine Mounts and Bolts

Worn engine mounts make the loudest rattle during start-up and acceleration. This problem requires professional help to diagnose.

Engine bolts and bearings of belt-driven components also produce rattling noises when they wear down. These issues aren’t critical, but I’d advise you to address them as soon as possible to reduce the likelihood of damage to other components.

Worn Piston and Cylinder

The phenomenon called piston slap can be the reason you hear rattling from your engine while driving at a slow speed. It’s caused by excessive wear of the cylinder and piston.

The piston moves as close as possible to the cylinder walls in the combustion chamber to increase effectiveness. The piston and cylinder walls wear with time, increasing the distance between them.

The rattling sound or slap occurs when the worn piston moves from side to side in the cylinder during combustion. Piston slap develops over a long period and often appears on old cars.

Identifying Piston Slap Sounds

Piston slap is unique in that it doesn’t produce other immediate symptoms: you only hear an infrequent rattling sound from the engine bay.

Therefore, you may need the experienced ear of a mechanic to diagnose the problem. To confirm piston slap, the mechanic may need to dismantle the engine and check the pistons.

Unfortunately, piston slap can cause faster wear of the piston rings, causing oil leaks into the combustion chamber. Blue smoke coming from the exhaust points to worn piston rings.

Experts advise that you ignore piston slap due to the complexity of the job involved in diagnosing and fixing the problem. Wait until the issue causes other problems and invest in an engine rebuild.

2. Leaking Engine Fluids

The transmission fluid and engine oil have minimum levels they shouldn’t cross. If these levels get too low, you may hear a distinct rattling noise.

Leaking Transmission Fluid

An adequately lubricated transmission should be silent; a non-lubricated one produces rattling noises.

If you hear rattling originating from the gearbox area, complete the following steps:

  1. Stop the car completely.
  2. Wait for the car to cool.
  3. Check the transmission fluid level.
  4. Top up the fluid if it’s lower than the level prescribed by the manufacturer.
  5. After topping up, visit a mechanic to plug the leak. Low transmission fluid levels can damage the gearbox, so it’s essential that you swiftly get the problem checked out.

Low gearbox fluid levels reduce the longevity of the torque converter, which, if damaged, also produces a rattling sound at low speed. Therefore, if you delay, you might have to replace a gearbox and a torque converter.

Leaking Oil

The engine pump on your engine distributes oil to wherever it’s needed in the engine. If the oil dips too low, it pumps oil along with air through the engine.

This may cause a ticking or rattling noise to come from the engine.

Low oil levels can cause extensive and expensive damage to your engine. If you suspect low oil levels, confirm how much oil you have left using the dipstick.

Top it up before heading to your mechanic to identify the leak’s source.

3. Loose Exterior and Interior Connections

Loose connections in your car, especially those in the brake and steering area, can cause rattling sounds.

Identify the Cause of Loose Connections

The brakes in your car are often fitted well when they’re new. However, you’ll need to replace the brake calipers after a while.

Loose installation of anything brake-related can cause an unpleasant rattling noise. If you hear a rattling noise after a brake service, chances are your mechanic didn’t fasten something properly.

Similarly, if you notice a rattling noise after any trip to the mechanic, the chances are your mechanic’s to blame. Refer the car back to them and direct them to the source of the rattle.

The steering column and its components are made from pretty hardy stuff. However, they will become worn and produce a rattling sound with time.

Damage to the steering requires professional input to diagnose.

Finding Loose Connections in the Car Interior

The rattling you hear might emanate from something loose in your car’s interior, in which case, the problem isn’t serious. Nevertheless, the noise can be unbearable.

As the car moves slowly, touch the surfaces near the sound’s source. The vibration should guide you to whatever interior connection needs fastening.

The noise may also come from loose items that have made their way into crevices in your car. Loose change in your glove box can make a disturbing noise, especially on a bumpy road.

To remedy this minor issue, empty the interior of anything loose that may move about and cause the noise.

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In Summary

The rattling noise your car makes can point to a serious issue or an insubstantial matter like some loose change. Generally, rattling noises coming from the exterior of your vehicle require more urgent attention than those emanating from the interior.

You can diagnose a rattling problem on your own, but most of them require professional input to remedy. I advise that you visit a mechanic as soon as you notice the rattle to prevent the worsening of a potentially minor issue.

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