Why does my car engine rattle when idling?

This blog post will answer the question, ‘Why does my car engine rattle when idling?’, and cover topics like reasons behind a car engine making rattling sounds when idling and their consequences, how to fix a car engine making a rattling noise when idle, and what every car engine sound indicates. 

Why does my car engine rattle when idling?

These are the following reasons behind a car engine making a rattling sound while idling:

  • Engine heatshield coming loose
  • Inadequate engine oil resulting in poor lubrication of engine components
  • Damaged timing belts
  • Damaged or broken engine mounting bracket
  • Dismantled serpentine belt
  • Damaged flexplate, in case of automatic transmission cars
  • A broken crankshaft balancing mechanism
  • Damaged cooling fan clutches

Reasons behind a car engine making rattling sounds when idling and their consequences

These are the following reasons behind a car engine making sounds when idling along with their respective consequences if they are not fixed immediately.

Engine heatshield coming loose

This is a possible cause for the car engine to make a rattling noise when idling. The heat shields are made of aluminum sheets and thus are prone to rust, causing the bolts that hold them in place to loosen.

This results in the heat shield popping out and flapping, creating a rattling noise when idling.

Muffler problems

A defective muffler should be checked or replaced immediately as per the requirements as it can make the engine run louder than usual. A muffler defect is usually identified by the formation of more fumes than usual and a sudden drop in car mileage.

Leakage in the exhaust manifold

A leakage in the exhaust manifold needs to be repaired with immediate effect and is indicated by the check engine light turning on. Leakage of the exhaust manifold can be very dangerous as the exhaust gases discharged from the cylinder are extremely hot and can damage parts made of plastic.

The exhaust gases can also be a potential threat to the car passengers as leakage in the exhaust manifold can cause the seepage of dangerous carbon monoxide and nitrous oxide waste into the car cabin and poison the passengers, they can also be fatal at times.

Defective engine bearings

This is another important issue that needs an immediate fix if it arises. Faulty engine bearings are easily identified by a significant knocking sound that can be heard coming from the hood. 

If these defective engine bearings are not taken care of soon, they might cause excessive knocking and finally end up seizing the engine. This issue needs to be consulted with a professional technician and the bearings need to be replaced immediately.

Low engine oil

A problem of low engine oil in the car is indicated by a rigorous grinding sound from the engine. In case the oil in the car is indicated by a modern oil indicator sensor and it still shows the oil level is sufficient, there might be something wrong with the sensor.

However, in the case of an old car, the oil level needs to be checked manually and it is advisable to check and refill the tank on a regular basis or conduct an engine tuneup process in case of emergency.

Torque converter turned old

This is a problem only observed in cars with automatic transmissions and is indicated by a grinding sound coming from the engine. The main reason behind this is insufficient transmission fluid or faults in bearings. This problem needs to be consulted with a professional immediately.

How to fix a car engine making a rattling noise?

These are how to fix the diagnose the various causes of an engine making a rattling noise:

  • In case of damaged or broken timing belts, it is best to replace them immediately as they are crucial for monitoring engine timing
  • If the catalytic converter is clogged or damaged, it must be replaced immediately as it will increase the volume and the potency of the exhaust gases.
  • In case the mechanism for lifting the valves is broken, the valve clearance can either be readjusted or by replacing the entire mechanism
  • In case of a damaged flex plate for cars driven by an automatic transmission, the transmission line needs to be removed before the plate can be repaired or replaced.
  • If the crankshaft balancing mechanism is cracked or damaged and cracks appear on the crankshaft, a bearing readjustment can solve the problem.

What does every car sound indicate?

These are some characteristic sounds that are produced in cars and their underlying meaning.

A whistling sound

These whistling sounds generally can be heard from under the hood. There is an almost continuous flow of air and coolant within the engine, and sometimes this continuous flow can form holes in the transport hoses. When air escapes through these holes, they create a whistling sound.

A ticking sound

Ticks and clicks inside the engine are a sign to check the engine oil tank or the dipstick meter to check the oil level. The pistons are the ones that can cause the ticking sounds as they get noisy when the engine oil level drops.

A sputtering sound

This issue is often referred to as dieseling, this generally happens when the car makes a sputtering sound even after the ignition key has been turned off. 

This usually means that there is still some residual air-fuel mixture undergoing combustion and being ignited without a spark inside the combustion chamber. However, this is more prominent in older vehicles.

A whirring sound

If there are whirring sounds coming from the car engine, it is highly probable that the car has defective or worn-out belts. There are several belts in the car that run at high operating speeds over a linkage of pulleys.

With use over time, they can stretch out or crack, needing immediate replacement.

Loud sounds while turning

If the car experiences a loud sound only while turning, there is a high probability that the car is facing problems with the tires. The main reason can be as simple as low tire pressure or inadequate inflation.

However, in more serious circumstances, the issue can also be caused by incorrect wheel alignment or defective wheel bearings.

A loud idling sound

If a car engine sounds louder than it normally does, the problem can be caused due to compression difficulties inside the engine cylinder. Compression issues may arise from the burning of an uneven air-fuel mixture inside the combustion chamber.

A rumbling sound

If a car experiences a rumbling sound, the problem can be caused due to holes in the car muffler. They do not drastically affect the car’s performance but can pose a huge threat to the passengers inside.

This is because a leak can cause hot and harmful exhaust gases like carbon monoxide and other nitrous oxide wastes to seep through and enter the cabin, which can potentially fatally poison passengers.

Research has shown a Kia Optima engine that was running louder than normal and its consequent inspection.


This blog post addressed the question, ‘Why does my car engine rattle when idling?’.

We understood the various reasons behind car engines making rattling sounds when idling and their associated consequences and the ways to fix a car engine making a rattling sound when idling. Furthermore, every car sound and what they indicate have also been discussed. Please feel free to comment on the content or ask any questions in the comments section below.

Frequently Asked Questions (FAQs): Why does my car engine rattle when idling?

Why does my car sound like it’s overheating?

This sound is indicated by a hissing sound coming from the engine. This can be caused by an overheated engine or a potential leak in the engine coolant. 

What does an engine sound like?

The characteristic sound of an engine is similar to that of a jet plane and it can be heard louder as the engine is revved further.

What is engine knock sound?

A knocking sound of an engine can be heard from under the hood as a loud clunky sound or a sound that makes it feel as if something is striking the hood from below. Engine knocking is usually indicative of a faulty engine ignition system.