Most engine noise may not necessarily come from the top. It may come from some inner engine components. An observed piston knock for some moments in the engine may be cause of a cold piston and may cease when the engine becomes warm. This may be caused by a gap in between the cylinder and the piston. However a dull rumble knocking sound may signal a bad rod bearing which may lead to bearing failure and or rod breakage. Here are major inner engine noise.
- OIL PRESSURE: confirm that the oil pressure is ok. Iif the oil pressure is ok, then replaced your oil sending unit(oil pump).
- LOW OCTANE FUEL: This could happen when low octane burning fuel bulilds up carbon in the combustion chamber. Engine overheating, advanced igniton timing could contribute
- FLYWHEEL AND CONCERTER BOLTS: this could lossen and cause noise.
- BIG PISTON GAP: this could be because of piston-cylinder gap. Also ensure connecting rod bearings are not separated.