Strange One (noise)
 

About a month ago I posted info. about a noise coming from the right rear of my 1990 C4. Sounded like a combination of a belt squeak/vacuum leak. It only occurs,
after the engine warms up and the thermostat opens. So I figured it must be oil tank/oil circulation related. We pulled the oil tank and checked what we could see.
No kinked hoses(replaced a bad rubber mount bushing). The noise is still there.
So now I ordered a new tank pressure relief valve(top of tank). Thought that this could be faulty and causing the noise. Any other suggestions, or things to check would be appreciated.
T

I think I have the same issue with my 993. I have narrowed it down to the cooling fan hub bearing and/or the alternator bearing.

Funnily enough I suspect the same noise on my 964,

can I check the alternator bearing easilly, how much movement should I find by
gripping it with its belts in place