Rod bearing noise is a thumping noise or knock at the side of the engine block that is LOUDER when the engine is hot and goes away when the affected cylinder is shorted out. A is wrong because main bearing noise is constant and cannot be shorted out. A main bearing noise is generally deeper sounding than a rod bearing. Also, a main bearing makes an EVENLY spaced single knock while a rod bearing generally makes a double knock. B is wrong. A WRIST pin noise can be diagnosed by disconnecting spark plug wires one at a time. Should the noise in the engine immediately double in frequency, then it's a wrist pin. Should the noise merely diminish a bit, then probably a rod knock CAUSED by a loose bearing. D is wrong because piston slap noise disappears once the engine is warm. Piston slap could be caused by the piston skirt deforming under stress.

Rod bearing noise is a thumping noise or knock at the side of the engine block that is louder when the engine is hot and goes away when the affected cylinder is shorted out. A is wrong because main bearing noise is constant and cannot be shorted out. A main bearing noise is generally deeper sounding than a rod bearing. Also, a main bearing makes an evenly spaced single knock while a rod bearing generally makes a double knock. B is wrong. A wrist pin noise can be diagnosed by disconnecting spark plug wires one at a time. Should the noise in the engine immediately double in frequency, then it's a wrist pin. Should the noise merely diminish a bit, then probably a rod knock caused by a loose bearing. D is wrong because piston slap noise disappears once the engine is warm. Piston slap could be caused by the piston skirt deforming under stress.