the sound of knocking (as on a door or in an engine or bearing); "the knocking grew louder"

Rapid, rattling combustion, also called detonation.

1] Noise created by part movement in a loose or worn bearing. [2] A condition, accompanied by an audible noise, that occurs when the gasoline in the cylinders burns too quickly. This is also referred to as detonation.

Periodic noise from a worn bearing in an engine, caused by the reversal of the load as the piston changes direction.

Preignition. If the gasoline/air vapor in a motor's cylinders is too compressed, the heat produced will cause it to ignite without the aid of a spark. This uncontrolled combustion probably will not occur at the ideal moment to transfer energy and promote rotation of the crankshaft. In audible cases, the exploding fuel charge expands against a rising piston creating vibrations and an accompanying rattle.

A sound that occurs in the cylinders when the fuel/air mixture is ignited too soon and the subsequent explosion hits the piston as it travels up the cylinder on the compression stroke. Usually, it's due to faulty timing, low- octane gas, or fragments of burning carbon in the cylinders. Also called pinging or pre-ignition. It sounds like marbles rattling in a can and can be heard best when accelerating up hills. This sound can also be caused by impending mechanical failure within the engine due to extreme wear of a piston or bearing. See also four-stroke power cycle.