alt or compressor whine?

[Keith Lawyer]

Hi folks, vehicle in question is a '90 200tqw, recently purchased after
warping the head on my '89 200tqw (don't ask).  Anyhow, the new-to-me
'90 has an odd whine at idle, seems to go away once driving.

Finally had some time to look at it up close last nite and my
mechanic's stethoscope (sp??) seems to indicate it's either the alt or
a/c compressor.  The sound does not really change when the a/c is
engaged, which may or may not be relevant.  Of course the ....
tensioner??... between these two accessories carries the sound quite
nicely making it near impossible to tell who is the culprit.

I can only describe the sound as hi-pitched HUM or a low-pitched WHINE
with a bit of a WHISTLE/CHIRP quality to it LOL.  The po reports it has
been there for some time; I've heard screaming bearings before and it
really doesnt' sound like a bearing going out IMO (at least not like
it's going to go out anytime soon).  I did search the archives and found
quite a bit of talk of alt whines, but most seemed to report failures
shortly after, and it did not exist ONLY at idle....

So, has anyone else experienced this?  I will pull the alt belt once
time allows.  The a/c blows cold and the alt charges fine...

TIA,
Keith L
who now knows a water temp gauge is worth it's weight in gold - damn
multi-function temp switches!