Vibration and clunk on take up in reverse vr statesman

Hi I am new to this forum and would like to ask a question.
My statesman VR is shuddering in reverse until I hear a clunk as the slack seems to be taken up, we took it to a mechanic to find what the prob was, he put it up on jacks but couldnt seem to find the prob, id it is limited slip diff and both wheels are off the ground when put in reverse should both back wheels spin as just one was turning, but when put in drive both wheels turned, the mechanic is pointing to the diff, maybe the culprit but before I shell out more cash I would like to ask for some advice or suggestions as to what it is, there is no power loss in the gear box, its an auto box thats been serviced, can someone please give me some advice
Cheers
Paully2012

 

Thanks for getting back to me Nick, Im at a loss as to what it is, when you put in reverse and start to go backwards the car shudders then a clunk as it is engaged but shudder pulls out with more acceleration, forward gears are perfect which leads me to think it may be the limited slip diff. when on a hoist only one wheel turns in reverse. I do thank you for your help Nick, could ou el me ow to check the diff oil in them as I cant find the inspection nut.
regards
Paul