[FC] click or clunk from differential?

[Wild8bill at aol.com]

I have a click or clunk sound that is correlated to the wheel rotating on  
the rear driver side. It is obvious when driving, but not too loud. This is 
a  new thing that appeared in the last few weeks. I thought it might be the 
wheel  bearing, but when I inspected it, the sound comes from the 
differential side of  the drive shaft, and only happens when turning the axle 
forwards, not backwards.  Any advice?
 
Bill
Richmond, CA