Help-Vacuum Leak/Slipping Belt Noise

["Pieter Van Dien" <pvd1@xxxxxxxxxxxxxxxx>]

I have a '97 E36 M3/4 that makes a noise similar to a belt slipping or a
vacuum leak when hot (after about 20-30 minutes of normal driving). The
hotter the car is the louder the noise to a point at which it tops out. This
problem first developed in October or November of last year. My local dealer
has made three attempts at a fix.

First, they applied belt dressing. Next they replaced the VANOS system and
all related gaskets and seals. Finally, they replaced the oil strainer for
the engine vent. None of this has changed the noise. They say they're
stumped and don't know what else to do.

No engine fault codes appear, which would seem to rule out a vacuum leak b/c
of the super-sensitive computer. If I turn the car off while its making the
noise and then turn it right back on, the noise goes away for a few minutes
and then returns. Anyone diagnose or repair a problem like this?

Thank you for any assistance with this annoying problem.

Peter

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