Today after i had an oil change, i notice a knocking noise coming from the engine. It only knocks when i accelerating. It kinda does it at idle but is very hard to hear. It sounds like it is metal on metal. I have taken my rods out twice. once to put new piston rings on and once to put new pistons in and i re-used the rod bearings each time. does this sound like rod knock. does rod knock happen when the rod bearings loose their clearances and slap up against the crank shaft? Or could this be detonation. I have never heard detonation before so help me out please.