as always, without hearing ourselves its difficult for any of us to diagnose.
firstly I will say I have known Z motors be noisy, its mainly from the clutch area. seemed to be a design problem. try to hear with the fller cap off if its louder, oil may get thrown out.
secondly, as a tip. without a stethoscope, get a long screw driver and put the blade on different NON MOVING parts of the engine, put the handle against your ear. it helps pick up noises from different parts of the engine.
just re read post, did you put metal rod to your ear? screwdrivers are softer!!
still thinking waterpump impeller bearing or alternator.
