...I was finally able to trace the problem to the accessory-belt tensioner. The dealer confirmed that this was the problem and replaced it. Not a peep out of it since.

<A HREF="Mailto:andy_hedin@hotmail.com">Andy Hedin</A>
'97 A4 1.8Tqms, Garrett 1.0 Bar, ABT Filter, Borla Exhaust, Euro Lights, more...

I would get a loud squeel, almost a howling sound, when it is realy hot. The dealer couldn't duplicate it, but felt it was a belt clutch of some kind. Andy Hedin's response sounds similar, and I'm going to ask my dealer to check out the accesory-belt tensioner.