Put simply, my rear end is on jack stands and I can see that both of the rear shocks have that oily residue, telling me they should be replaced. Since the car is jacked up with the wheels off, what else should I check? The knock comes right when I let off the accelerator (it's louder if the pedal is released suddenly or I was accelerating at a higher rate) and from the rear drivers side. It may be something that would happen at acceleration too, but my E300D is much better at slowing down. Right now I'm trying to compare left to right, but that isn't yeilding much. Brakes and flex disks are ok though.