8 Reasons Why Your Car Engine is Making a Rattling Noise

If your car engine is making a rattling noise, there is something wrong with your vehicle. An engine should always sound smooth. If your engine starts making a rattling noise, here are 8 reasons why it is doing that:

If your car engine is making a rattling noise on startup, idle, or when accelerating you could have a faulty serpentine belt tensioner, a loose bolt on the mounting bracket, loose timing belt, rusty or broken flexplate, faulty harmonic balancer, loose fan blade, engine knock(pinging) or low levels of engine oil.

Key Takeaway

8 Reasons Why Your Car Engine is Making a Rattling Noise

  • Low engine oil
  • Cracked or broken serpentine belt
  • Broken mounting bracket
  • Broken or cracked timing belt
  • Broken flexplate
  • Broken crankshaft harmonic balancer
  • Faulty fan clutch
  • Engine knock or ”pinging”

8 Reasons Why Your Car Engine Making a Rattling Noise

8 Reasons Why Your Car Engine is Making a Rattling Noise

A car engine has to make some kind of noise. The engine has many moving parts which all make some kind of noise. But all of this is normal. However, if your engine starts making a rattling noise, that is far from normal. Here are the top 8 reasons why your car engine is making a rattling noise:

1. Low Engine Oil

8 Reasons Why Your Car Engine is Making a Rattling Noise

If your engine is making a rattling noise, the first thing to suspect is low engine oil. If your engine has low oil, it can cause rattling sounds due to poor or no lubrication for vinyl engine components.

Engine oil is used to keep components lubricated and prevent damage due to friction, and as the level drops, more metal-to-metal contact can occur which causes vibrations that translate into the telltale rattling sound.

Check engine oil level and add if needed. If the engine oil level is really low and the engine is rattling after the oil has been added, permanent damage could have occurred and replacement is needed for whichever part is been damaged.

2. Cracked or Broken Serpentine Belt

8 Reasons Why Your Car Engine Making a Rattling Noise - Broken or Cracked Serpentine Belt

All diesel or gasoline cars have a serpentine belt. Some have one, some have two or three. The serpentine belt has a function to drive your alternator, water pump, and air conditioner compressor. Very often the serpentine belt is mistaken for a timing belt. The difference is that the timing belt runs the engine camshaft and in most cases, you cannot see it because it is hidden under protective covers, whereas the serpentine belt is visible.

When the serpentine belt gets cracked or completely broken, it can make a rattling noise because it will get loose and hit vital engine components.

If the serpentine belt breaks, your engine would start making a rattling noise. The car won’t be drive-able and you would have to call a towing truck. If you drive your car with a broken serpentine belt, the engine would overheat because the water pump won’t work.

3. Broken Mounting Bracket

8 Reasons Why Your Car Engine Making a Rattling Noise - Broken Mounting Bracket

The third thing that could be making a rattling noise is a broken mounting bracket. Mounting brackets are used to support various accessories such as the power steering pump compressor and air pump, as well as to attach the engine to the vehicle frame.

A broken or worn mounting bracket will allow the engine to move freely, creating vibration and rattling noise while running.

If one of these mounting brackets is broken, the component that the bracket is holding will start to vibrate and make a rattling noise. You would need to check every mounting bracket nut or bolt to make sure that there is nothing loose.

4. Broken or Cracked Timing Belt

8 Reasons Why Your Car Engine Making a Rattling Noise - Broken or Cracked Timing Belt

The timing belt has a function to connect the engine crankshaft to the camshaft which allows the valves to open and close at the correct timing with the position of the pistons. The timing belt has to be under certain tension which is allowed by a timing belt tensioner.

A broken timing belt may cause the engine to make a rattling noise because the timing belt synchronizes the camshaft and crankshaft of an engine, allowing them to communicate with one another seamlessly. When the timing belt is broken, however, this communication is hindered or disrupted, causing mechanical components to work against each other rather than with each other which produces a rattling sound in the process.

If the timing belt or the timing belt tensioner gets damaged, it will get loose and will start to vibrate and make a rattling noise. You must always change your timing belt if you notice any cracks to avoid any additional damage to the engine.

5. Broken Flexplate

The flexplate or a flex-shock device is found in cars with automatic transmissions and has a function to connect the crankshaft to the torque converter and improve smooth running.

A flexplate is an integral part of any car with an automatic transmission and serves as a connection between the engine and the transmission. Its purpose is to absorb vibrations, but if it weakens or cracks over time, it can start making rattling noises.

If your vehicle has a broken flexplate, the connection between the crankshaft and the torque converter would be compromised and it won’t run smoothly. The flexplate will start to wobble and will most definitely produce rattling noise. If this is the case, you would have to remove the flexplate cover. Then, check for rust, cracks, or missing bolts.

6. Broken Crankshaft Harmonic Balancer

The crankshaft harmonic balancer is part of the crankshaft. It has the function to absorb and reduce vibrations from the engine as the crankshaft rotates. It is made of rubber and metal and can be found at the front of the crankshaft pulley.

Rattling noises are often caused by a broken crankshaft harmonic balancer. It is located between the crankshaft of the engine and a pulley, usually at the front of the engine. The main purpose of this part is to reduce vibration and noise levels. So, if it breaks or becomes worn down over time then it will no longer be able to do its job properly and rattling noises will start emerging from inside the engine compartment.

If the rubber and metal on the crankshaft harmonic balancer wear or get dislodged it would make a rattling noise and cause engine vibrations. It is an expendable item and at some point in time, it would fail.

7. Faulty Fan Clutch

8 Reasons Why Your Car Engine Making a Rattling Noise - Faulty Fan Clutch

The fan clutch is a component of the cooling system that regulates the engine temperature by engaging and disengaging the engine cooling fans. Some vehicles have mechanic fans, and some had electric fans, but they both operate based on engine temperature. Once the engine temperature gets high, the thermostat triggers the fan clutch which engages the cooling fans.

If the fan clutch is faulty and gets stuck in an engaged position, it will turn on the engine fans even when they are not needed which will create a loud noise. If the cooling fans run for a longer period of time, they can get loose and start creating a rattling noise. Open up the hood and inspect the fan blades by checking for excessive movements.

8. Engine Knock or ”Pinging”

8 Reasons Why Your Car Engine is Making a Rattling Noise

An engine knock or pinging occurs when the mixture of air and fuel inside a cylinder is incorrect or unbalanced which makes the fuel burn unevenly causing shock waves at the wrong times which is making a rattling noise and can damage the cylinder wall or the pistons.

Basically, when an uncontrolled explosion happens in the cylinder it can sound like an audible rattle. Most cars have knock sensors that control this condition. But, if the fuel octane levels are too low it will persist anyways. If the problem keeps happening, the engine could have carbon buildup.

Igor Iwanowski

I am a certified Automotive Service Excellence (ASE) mechanic since 2018. I specialize in Brake systems, dashboard warning lights, EGRs, general engine problems, EVAP and Emissions issues.

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