What does a rod knock sound like?

A rod knock usually sounds like a light, steady pounding noise coming from inside the engine block. It is loudest when the engine is running at higher revolutions per minute, and when the vehicle's speed is steady, neither accelerating nor decelerating.

Once the sound of engine knocking has been confirmed as a rod knock, it is possible to narrow down which rod is causing the problem by performing a cylinder balance test. This test is conducted by cutting the power to each spark plug in the engine in turn. When the spark plug associated with the knocking rod loses power, the sound should decrease.