[s-cars] Weird noise at WOT

[Marc Rhatigan]

Hi -- Sorry to drop in here with nothing but problems, but y'all are the
best, so here goes...

My '97 (Canadian) S6 sounds like a cross between a vacuum cleaner and a
dentist's drill between 3.5K and 4.5k at WOT. Definitely engine-vacuum
related; doesn't happen with no load on the motor.

Also doesn't happen -- or perhaps much more faintly -- at 3/4 throttle
through the same range. Acceleration much smoother at 3/4 throttle; perhaps
a little more power than at WOT, too(?) Oddly, the engine seems fine
otherwise.

I have the MTM Stage III set up. Any ideas? Wastegate? Airbox? Intake leak?
Thanks, all.

Marc Rhatigan