Don over the years I've had some engines with noises that really had me pulling my hair out.

An enginge knock that turned out to be the oil baffel in the valve cover coming loose and being hammered by the rockers.

A noise deep in the engine that turned out to be a crank counterweight hitting in one spot on the custom pan.

A noise that sounded like loose lifters that turned out to be the mechanical fuel pump coming apart.

A couple of cracked flex plates that sure sounded like rod bearings when you first listened to it.

I guess what I'm getting at it that you don't want to overlook the simple stuff while you're tracking down the problem.