Loud whining 86 Z24 engine

I am hoping someone here can help. I have a 86 nissian kingcab 4X4 with a z24 engine w/ 154k on engine. I have a horrible whining noise that is getting worse and worse in/on the engine. It sounds like a mosquito buzzing around when I give it gas but a 100x's louder. At first (about 4 months ago) it would only do it for a while when I started it up but it is doing it all the time now. It runs great, good gas milage, etc. It is just that noise. Does anybody have any suggestions on what I start looking for? Could it be vacume or catilitic converter? If anybody knows please reply it is driving me crazy!

Thanks, Krocus

Where does it sound like the noise is coming from? Under hood, Middle, Rear??? My '87 has a howling Alternator bearing that one of these days I will get off my butt and fix.

UncleGus