disco rear axle onto 1986 LR90 Help!!

HI, can anyone advice me or fault find for me please . I have a 86 Land Rover 90 which in the process of rebuilding with 200tdi disco engine. However I have put a Disco rear axle on to. However, whilst driving, there appears to be massive graunching from the rear axle, especially upon engine breaking. I have changed the flange which connects to the prop and really could do with some advice please!!! Sorry if any thing is unclear.
Regards Kinson

I suggest that you check the pinion bearing in the diff for vertical play. Remove prop shaft first.