Vibrating noise

I had a similar problem and found the passenger side exhaust hanger on the crossmember was rattling. The H-pipe hangs on some very small hangers on these cars. The metal "loop" that houses the rubber bushing was rattling around. It is steel and is sorta crimped onto the aluminum crossmember. I put a small sheet metal screw in between the hanger and the crossmember. Worked 4 me. I dunno if that's your problem or not, but it's worth a mention