I have this exact sound coming from mine and I've been trying to track down the source for a couple of months now. When I put my intake on and the noise became 5 times louder, I thought it had to be the supercharger for sure and now I stumble across this thread by accident. Is there any way to quiet this down some? It is so bad that even my girlfriend asked what the noise was and she wouldn't here the engine fall out of her car. I would say it is probably a little louder than the video that Blue posted the link to. Is this really normal for these cars? My last GP was a GT so I'm assuming the IAC is different on the supercharged 3.8? A new IAC valve isn't that much but if this is normal, I have better things to spend money on.