Ok man im excited to hear the outcome! I hope it all works out cheaply.

 

Sorry for the extremely late reply. You have probably resolved your issue but I just to finish off this thread. Changing fluids did not fix it. I installed Megan driveshaft spacers and all is good now.

 

A thud or thumping sound from the rear can be caused by the LSD. Is the sound you hear when making low speed turns while the car is out of gear or costing? The turns only need to be slight such as a back and forth rocking of the steering wheel.

 

I had a simialar sound and found my gear and pinion had a few crunched teeth.
upgraded to a 4.44 and because the diff centre was fine it was all rebuildable with new bearing etc quite cheaply.