If the rear transmission mount on my 745t was bad would a hollow knocking sound be made when going over certain bumps? I can pull the rear of the transmission down, hear a knock and see metal to metal to metal contact between the trans and the cross member. Can I be fairly certain that this is the cause of the hollow knocking noise? Has anybody experienced or know of similar situations. Also, should I be able to move the drive shaft around in the center\mid drive shaft bushing\support enough to make clunking noises? Any help, comments, observations would be appreciated.

The hanger bearing for the driveshaft should allow no more than about 1/2 inch of play. I would say if you have over 150K on the car to suspect that first. If your driveshaft ever hits the tunnel or bangs under there, you may think about replacement. Mine banged for a couple of years before I changed it.

The tranny mount is relatively cheap, so I changed mine at the same time. You'll eventually need to change it anyway.

broken mount makes a roaring noise from transmission setting on crossmember