About half the time I start my 1993 968, there's a loud screeching sound that is exactly like a belt is slipping. The screeching lasts for about 30 seconds, reaching a crescendo and cutting off like someone flips a switch. Both belts (power steering and alternator/air conditioning) are good and snug. It's not related to the A/C, because it will screech with the A/C off.
Today, I was driving the car while it was doing its 30-second screech, and the screech got really loud and cut off. When it cut off, I could feel a distinct increase in power from the engine, as though whatever was screeching was loading the engine. Since I've ruled out the A/C, I figure that there's a problem with either the alternator, power steering pump or water pump. (The water pump is driven off the back of the timing belt.) Everything seems to work okay while the car is screeching -- there are no dash warning lights for a weak alternator and the steering feels fine. I can run the A/C or not run it, and it doesn't affect the screeching.
I have a few ideas about how to troubleshoot this but wonder if someone out there has experienced the same thing and can point me toward the problem. Thanks!