Read descriptions and causes of some common engine noises. Knocks, ticking, rattling and more.

Main Bearing Noise

Damaged or worn main bearing noise is revealed by dull thuds or knocks which happen on every engine revolution. This noise is loudest when the engine is under heavy load. Excessive crankshaft end play is indicated by an intermittent rap or knock sharper than a worn main bearing.

The following are causes of main bearing noise:

  • Low oil pump pressure
  • Thin, diluted or dirty oil and/or filter
  • Excessive main bearing clearance
  • Excessive crankshaft end play
  • Out-of-round crankshaft journals
  • Loose crankshaft pulley
  • Loose flywheel or torque converter
  • Loose main bearing cap

Connecting rod Bearings

A damaged or worn connecting rod bearing will produce knock under all speeds. During the early stages of wear, connecting rod noise may be confused with piston slap or loose wrist pins. Connecting rod knock noise increases in volume with engine speed and is at its loudest on deceleration.

The following are causes of connecting rod bearing noise:

  • Excessive bearing clearance
  • Worn crankshaft connecting rod journal
  • Thin, diluted or dirty oil and/or filter
  • Low oil pressure
  • Crankshaft connecting rod journals out-of-round
  • Misaligned connecting rod
  • Connecting rod bolts not properly torqued
  • The wrong bearing inserts or misaligned bearing half

Timing Chain and Gears

Engines designed with timing gears, or those equipped with a timing chain and sprockets, can produce different noise. The most common noise is a high frequency, light-knocking sound. This sound will generally be the same in intensity whether the engine is idling, operating at high speeds, or under load.

The following are causes of timing gear or chain and sprocket noise:

  • Worn timing chain and/or gears
  • Misaligned gears
  • Excessive backlash
  • A damaged tooth
  • Gear or sprocket loose on the shaft
  • Too much end play in the camshaft or crankshaft

Loose or improperly seated camshaft timing gears are usually loudest when warm. They are speed sensitive only. They are not load sensitive.

Cam gear noise will usually be evident at a warm idle in neutral and sounds much like a loose timing chain noise.

Piston Noise

Piston pin, piston, and connecting rod noise are hard to separate. A loose piston pin, for example, causes a sharp double knock usually heard when the engine is idling, or during sudden acceleration then deceleration of the engine. A piston pin that has been improperly fitted will emit a light ticking noise that is more noticeable with no load on the engine. Excessive piston-to-cylinder bore clearance will cause piston slap noise. The noise is similar to a metallic knock, as if the piston were "slapping" the cylinder wall during its stroke. As with most engine noise, understanding the cause of the noise will help you imagine what the noise sounds like. An indication of piston slap is a decrease in noise as the engine warms up. When the engine is cold, the piston to bore clearance is greater and piston slap will be louder.

Flywheel Noise

A loose or cracked flywheel will produce an irregular thud or click. To test for a loose or cracked flywheel, operate the vehicle at approximately 32 km/h (20 mph) and shut off the engine. If a thud is heard, the flywheel may be loose or damaged. This type of thud is loudest on deceleration. Loose torque converter-to-flywheel or flywheel-to-crankshaft bolts will sound similar to bearing knock. This condition produces several raps during quick acceleration on a free running engine. Depending on the idle smoothness, when the transaxle is in gear, the noise may or may not appear. Check the torque converter-to-flywheel and the flywheel-to-crankshaft bolts before attempting to investigate any bearing-related knock.


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  • Guest - Jeffery Smith

    My 1996 GMC Jimmy truck has a knock when I tighten up the flywheel it stopped knocking but the other day I drove to the store and it stopped on me and would not crank anymore it was only clicking on the turnover not fully turning and I was trying to see the anyone know what that problem could be

  • Guest - 98 Sable Problems with Engine

    What is suggested to do to fix the following things wrong? Backfiring when starting and while accelerating, very low power accelerating, bad gas mileage, and timing off.

  • Guest - Ann Jones

    In my 2004 Avalanche i hear a tapping noise in first gear and then slightly worse in second gear. It completely disappears when im traveling down the road. Should i be concerned about this immediately?

  • Guest - Elizabeth Norton

    I have an 89 Ford Taurus wagon and I noticed a "ticking" noise coming from the fuse box under the steering column. Later in the day the battery was dead. I charged up battery and then noticed a "ticking" noise coming from the inside panel area in the cargo area in the back on the Drivers side. After a while I heard my car doors lock. The next day my battery was dead again.I had the battery checked out and it is good. The car will drive fine. I unhooked the battery cables for now. If the battery goes dead and it locks the doors I can't get in the car with the key. I had to use a slim jim to open a door. Now I keep a board under the hood when it is parked at home to create a little area so the hood won't latch so I can get to the battery if it goes dead. I have had about everything replaced on this little nightmare and it looks like a new car. I want to know what this problem is so I can get it repaired and then sell it. Any ideas? Thank you.