I've had my GT since May, and there is one persistant buzzing/rattle at about 1200 RPM, in any gear. It sounds like it's a harmonic vibration of something near the A/T torque converter. I haven't had the dealer look at it yet. Mostly, I just go to a higher RPM ASAP.
I did have another more regular buzzing on slightly rough roads. It was driving me crazy. It turned out to be my garage door opener had a loose battery and circuit board. I had it clipped to the sun visor and it put out a buzz. I used some silicone caulk to pin the board and battery down - - - no more buzz. YMMV
I did have another more regular buzzing on slightly rough roads. It was driving me crazy. It turned out to be my garage door opener had a loose battery and circuit board. I had it clipped to the sun visor and it put out a buzz. I used some silicone caulk to pin the board and battery down - - - no more buzz. YMMV