'76 300D Not the rear brakes - more serious

Well, I had hoped my problem would be so simple but i was totally off! Upon more careful examination (parking brake shoes and adjuster are o/k), this noise is coming from under the car and is not directly related to the brakes! Although applying the brakes in reverse will cause the symptom, so will hitting the accelerator. In fact, it seems any sudden application of torque to the driveshaft will create this noise. I now suspect either the universal joint or the center support bearing! I also assume that as this problem gets worse, it will begin to make noise in drive as well as reverse?! Can anyone think of a way to narrow down the problem between the u-joint and the support bearing?? Either way, this noise is definately driveshaft related, and is coming from somewhere between the center to the rear of the car. And can anyone guess why such a problem decides to show itself in reverse first, as opposed to all the time? Are the wheels torqued more in reverse than in drive at very slow speeds? Thanks again
-travis


------------------
'76 300D