Engine Noises

Step 4 - If a heavier noise seems is being generated from the lower half of the engine, the problem can be more serious and disassembly maybe required. But, sometimes a lower engine noise could be generated due to excessive carbon, (carbon is a natural byproduct of the combustion process which builds up on top of the piston.) This knocking noise is created when carbon is compressed between the piston and the cylinder head. To repair this problem the cylinder head needs to be removed.

Step 5 - Some engines are manufactured with a timing belt. This belt is kept under tension by the belt tensioner. The belt tensioner is constructed with a bearing that can sometimes fail, creating a squeaking noise or chirping sound. Also, when this tensioner or timing belt starts to fail it can cause the timing belt to misalign. This condition will cause the timing belt to shred producing ticking/scraping noises inside the timing belt cover.

Step 6 - A flex plate is used in automatic transmission applications. Its used to connect power form the engine to the torque converter of the transmission. When a flex plate fails it usually cracks at the crankshaft mounting bolts. This will make little to no noise at idle, and make more noise depending on how much load the engine is under. The more throttle that is applied the louder the noise will become. To check for this condition remove the flywheel inspection plate or cover. Using a small flashlight and mirror, check for signs of rust dust near or around the bolts. Rust dust indicates a break or crack. Its these cracks flexing back and forth that generate the ticking noises. Replacing the flex-plate requires removing the transmission.

Step 7 - The IAC motor (idle air control) controls idle air to the engine. When an IAC motor fails it creates a loud humming sound when it fails.

Step 8 - Some engines are equipped with a cam angle sensor. This particular sensor is basically a distributor housing with a sensor and trigger plate mounted to the center shaft. If the sensor seizes due to lack of oil a high pitched squeaking noise will be produced. To check for this condition remove the serpentine belt and restart the engine. If the noise is still present suspect the sensor housing.

Helpful Information

Today's engines have been designed with more complexity and moving parts than ever before. Most of the time when you hear abnormal noises there is something going wrong. Excess engine noise is due to excessive clearance between two internal metal parts that should have little to no clearance. This clearance can be due to many things from a broken valve spring to a crankshaft bearing that has failed. The first step is to identify where the engine noise is being generated, with the engine running isolate where the noise is coming from in the engine, either the upper half, lower half, front half or rear half. (note: listen from above the engine or below the engine as this will help determine where to start looking for the cause of the noise.

Crankshaft Bearing

Best Practices

  • To avoid engine noises change your engine oil every 3,000 to 5,000 miles with normal motor oil, and 6,000 to 8,000 miles with synthetic oil.


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2015-01-12)