[Kurt in NJ]

Louder cold or warm ----- piston slap tends to quiet as pistons warm---- wristpin noises tend to get louder as engine warms and is sort of a double noise usually

"No metal in the oil"?--- has the oil been drained-- and no pieces in the recess of the drain plug----- the pan is off and no debris--- or I rubbed the oil on the dipstick between fingers and it still feels oiled not gritty

Is it louder on reving up or as it coasted down from reving up?

My guess would be center main ----- but not hearing it in person--- it's only a guess