need help
 

I have an 87 IROC with a 700R tranny and a Borg Warner 9 bolt rearend. I am hoping to keep it as original as possible. Anyways where my problem lyes is after the car is warmed up , when you step on it of the line even alittle I get a bad grinding almost a lock up feeling and a nasty grinding sound from under the car. I have had a few different mechanics look at it, but because Im from Canada nobody has ever seen a 9 bolt rear end before. Not 1 answer the same. Plz help