1981 w123 diesel rear end knocking
 

The car has 75k from new (!). The SLS system has been overhauled and works perfectly and has new accumulators. The sway bar mounts and control links are new. The diff mount is new.
When I go over smallish bumps there is occasionally a dull thunk from the rear. Riding in the back it seems to be more central than on one side and almost sounds like the entire rear axle is loose. The front mounts for the sub-frame are new as well btw. The flex disks are almost new too.
Does anyone have ANY ideas what I can check next. Using a crowbar I can't find anything that moves underneath either.
thanks

Check out your trunk for loose spare or tools.

It could be that the axles need to be shimmed. Grab them and see if there is any movement in and out of the differential. It doesn't take much to make a clunking sound. Search on here for axle shims. If you just changed axles your old shims may still be on the old axles, otherwise they are available from the dealer.

another thing to check could be the ball joint that connects the sls strut to the trailing arm

I Want To Learn
 

...So I subscribed to this thread .