Odd Thud ~ and its not sheep falling out the back

Bit of advice please guys,
Had trouble disengaing the diflock a couple of weeks ago.
But managed it in the end. 250 yards in reverse
I now appear to have an odd 'clunk/Thud' at the rear end when not being smooth with the gearchange!! also if I select reverse and don't soft shoe the clutch.
Vehicle is a '95 300 TDI.
Whats it likely to be , any idea's is there a UJ back there?
Not had a chance to get underneath, but is there an easy way to check the drive stuff. There's only me.
How by the way, as far as I'm aware all original bushes and when I bought it there were no 'new' ball joints etc fitted., but shocks have been replaced.
Thanks guys.

Have you got a rubber 'doughnut' joint in the rear prop, could be that.

or the A Frame ball joint.

Thanks guys.
I'll have a look for a doughnut tonight and see if I can get a view of the bearing/joint.
Will let you know the outsome
TH