[Healeys] Rear end clunk

[MGTD51]

My BT7 has a clunk in the rear end just behind the drivers seat.  It 
does not happen when I am driving on a smooth road, but when the road is 
bumpy it does.  I have replaced the shocks and they are tight.  The 
Ubolts are tight as is the panhard rod.  The springs seem to be fine and 
I can find no evidence of any damage/marks caused by the suspension 
hitting the bottom of the car.  The exhaust is tight.

Is it possible that the Ujoints are bad and they only clunk when the car 
is bouncing a bit?

Larry Swift