Diagnose engine problems by engine noise by first becoming familiar with the way the engine sounds when it is running properly and then recognizing the pattern and pitch of the noise being made. Clicking or chatter that disappears at higher speeds is often caused by the valvetrain. Knocking or pinging noises are a symptom of detonation occurring. A light knock or pounding noise is a symptom of connecting rod issues.
Faulty piston pins cause noises similar to those generated by an improperly tuned valvetrain and can be identified by a metallic double knock noise at idle. A cylinder-balance test, which shorts out each culinder's spark plug one at a time, is a good way to determine which problem is affecting the engine. The offending cylinder ceases to generate noise once the corresponding spark plug stops delivering a spark.
Heavy metallic knocking, especially when the engine is accelerating or under load, is indicative of problems with the crankshaft assembly. A rhythmic and rumbling knock is a sign that the main crankshaft bearings are worn and in need of replacement. A distant-sounding knock could be rod bearings that have become worn or damaged. An irregular and sharp sounding knock is usually the crankshaft thrust bearing failing. Crankshaft problems should be repaired as soon as possible to minimize and prevent damage to other parts of the engine.