Hi I am in a bit of a pickle (aren't I always).
Currently have my right hand side wheel jacked up this happens on the other wheel too I think but when I start the car and put it on reverse and let go of the clutch when the engine is idling as the axle starts to spin there is a bad rumbling and clanking noise, I cant quite tell if its in the differential.
It must be, but, as I rev the engine and when the axle spins faster the noise goes off I have the back cover of the differential off and the brake disk off.

I remember when the car was on the ground and if you would keep reversing backwards there would be a noise like something is getting jammed and jumping inside along with the clanks and rumbling this mostly happens on idle I think and on the 3rd gear as well i cant see anything getting jammed or anything i don't thing the propeller shaft is hitting anything and it cant be the gear box although the car is temporally converted to a manual.

Any ideas bad bearings the CV joints look good but i am no expert probably the drive pinion etc all feed back will help a lot,

The car is a 1975 240D W115 2nd version.

Thanks Jeremy.