I also have a noise like this, though I am not sure if it is the transmission mount. I noticed this noise after I installed my long tube headers and the y-pipe. My original thought was that the y-pipe was banging on something, because when I ran it open headers I didn't (or couldn't ) hear the banging. I went under the car and it has about 1/2" clearance from the frame on the driver side header, and then about 1/2" clearance from the y-pipe to the torque arm, but those are the only critical spots. I can't bend the pipe at all. Do you guys think this could be the torque arm hitting the y-pipe, or the headers shaking and hitting the frame? It only happens under hard acceleration in 1st and 2nd gear. Or is is possible that the added power that the headers gave me just killed my tranny mount?

 

Stock tranny mounts on 4th gen F-bodies suck.