Clunking at rear of car...

[Curt Onstott <fungus@CSOS.ORST.EDU>]

I've noticed a clunking in the rear end of my '70 Midget.  I used to hear 
the same clunk in the rear of my MGB.  I've checked the wire wheels of 
the midget and there isn't much slop.  The clunk can be heard when I 
begin moving forward after having been in reverse and sometimes when 
taking off from a standstill.  I can feel some slop in the rear 
differential when I rotate the driveline.  Is this "clunking" normal, or 
is there something else I should check?