I checked the heat shield on both the OE header and the Cat. Neither was loose or causing a rattle, but I still hear the noise. Last night, I tried to get a sound clip of the noise while driving the car, but all you could hear was wind, intake noise and distortion. At this point, I'm thinking that it's not the cat or header heat shields and that it may be some kind of an exhaust or vacuum leak of some sort, or something internal engine perhaps. It's tough to diagnose, since the car has to be moving down the road to really hear it and you can't use a stethoscope to listen to specific areas under the hood unless its parked. I'm gonna check on Mitchell for TSB's for the Teg and see if there were any for these symptoms. Ideas?