I just bought a 1995 riviera supercharged and the guy that sold it to me said that he thinks it need a new supercharger. When the vehcile is idling a grinding noise is heard from the top of the engine. I originally thought it was just the alternator grinding. But it turned out not to be. The grinding noise is hard to pinpoint because nothing is vibrating when touched to pinpoint the problem area. Does this sound like a supercharger to you guys or do you think it is something else. The vehicle has 65000 miles on it and drives great . do the superchargers act up like this when they go bad or does someone think I have a different problem. Also when i turn the vehcile off the grinding noise is heard louder for that second that the vechicle is turning off. Any info would greatly be appreciated.