Another W126 Driveshaft Question

[raymr]

I'm getting a vibration at 60+ mph. The flex disks and universal joint are OK. I can shake the driveshaft assembly about 1/4 inch back and forth at the center support, and I guess this is due to the rubber mount surrounding the bearing.

There seems to be some play between the front and rear driveshaft halves. When I turn it back and forth or shake it, there is a metallic ringing noise that seems to come from the front half. Is this a likely problem?