1976 Porsche 911S - stretching sound at idle on 1990 Porsche 911

Every time I start my 76 911 (with the idle at 1000 rpms), I start to hear a stretching sound that seems to be coming from the fan/alternator area. As the stretching sounds, the rpms go from 1000 to 3000/4000. The fan belt is new/ and tight. I just bought the car recently and the previous owner told me this has never happened to him and that the car was recently tuned up at a Porsche dealer before my purchase. Here is a youtube video (not my car) but another car making the same sound.

http://www.youtube.com/watch?v=6djlBOFPgc4

Any help would be greatly appreciated -

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1 answer
This is actually a common problem after belt replacement. The most likely cause is that the belt is too tight. Check the belt tension with the engine off, there should be some play to it. If it feels very tight, have it adjusted to be a little looser.