Uh Oh. I just experienced several "clunks" from the rear end of my 97 M3. After the first one, my first reaction was that one of my kids had put a bowling ball in my trunk. The second made me head for home. This is not the kind of sound or feel from an unlubricated CV joint, but seems to be coming from the differential. It is a singular thump and shudder in the drive line that seems to occur under positive load and is proportional in severity to the amount of torque applied. It also seems to happen in both turns and straight line situations. It did not occurr, however, as I coasted for about .5 miles in a long gradual down hill section of the drive home. It did occurr as I gently drove up the following hill. When I reached my garage, I reversed into the driveway quickly and restarted quickly back into the garage in a straight line. This resulted in the most violent result of all. I raised the rear of the vehicle. All suspension and drive line components seem to be secure. When I spin each wheel alternately, it spins the oposite wheel in the oposite direction, but with no noticeable interference or noise. Oh yea, the fluid is tired, could this be the issue?.....What now?