Clunk from rear

Hi,
I am trying to find the cause of this issue and was looking for some help. The truck is a 2007 X3si.

If I slow down to 0-5mph and then take off, I get a clunk from the rear of the truck. Same thing sometimes happens when I take off from a complete stop. It does not happen when slowing down to higher speeds.

The car had a new rear diff installed for other reasons and the problem is still there.

Any ideas on what I should be checking?
Car has new rear brakes for what it's worth (problem was there before and after brake change).

Thanks