I have a '92 400e with about 125k on the odo. A noise I've never heard before surfaced. Immediately upon starting the car there is a grinding noise eminating from underneath center of the car. It sounds like a box of rocks being ground up. Increasing revs makes it louder. It is louder when heard from the right side of car than the left. It sounds like its coming from an area between the output shaft of the trans but before the differential. Driveshaft, maybe?

With the time crunch of the holidays I'm looking for a little advice that might get me homed in a little quicker on the cause and cure. Any help would be much appreciated. TIA.