Rear wheel bearings generally get noisy (hum or if really getting bad, growl. Thumping is not characteristic of a bearing, although, I suppose anything is possible. Pinion is not likely as it is usually turning 3 to 4 times faster than the wheels (depends on final drive ratio) and failure mode for that component is generally a pronounced whine or hum. (check backlash). If you have any rubber coupling discs in that rear end, they would be suspect. If you have replaced both half shafts, then I would look at the rear end suspension components. Possibly the carrier bushings and any other locating components in the rear end. U-joints should never normally make contact with the frame as the nest (center section) is bolted to the frame. Start at the outermost parts of the suspension and work inward. You have more than one u-joint in that car. With independent rear suspension, there are at least 5 variable geometry drive components you should check, be they u joints, cv joints or rubber couplings. Depends on car and model. A rythmic metallic thumping sound like something worn or out of balance. Hope this helps...
[This message has been edited by jeffsr (edited 01-24-2000).]