I have a 82' 280ZX (non turbo) which has a bit of noise & vibration going on
with the 5 speed transmission. I'm trying to isolate it to the most likely
source before I make any decisions on how to proceed. Basically the problem
presents itself like this:

I start the engine and put it in neutral, and there is a low whine coming
from the front of the transmission which can be felt through the stick. It's
not terrible, but absolutely noticeable. If you press the clutch in, the
noise and vibration disappears. The effect is the same while driving only
worse as the whine turns into a slight grinding which also goes away with
the clutch disengaged. It does not seem to matter what gear I'm in. Also the
clutch seems tight and is not slipping at all...

Everything I've read suggests that it's the front bearing supporting the
input shaft of the transmission. But I've also read that it could be the
countershaft bearing. I've replaced the clutch on my 79' 280ZX years ago and
didn't find it too complex (just alot of labor), but I have no experience
working on or diagnosing the transmission itself.

Does anyone with a little more transmission experience have some hints?

Thanks!

Chris