3.55:1 rear end noise, is it normal?

[Mo65]

I have one question. I had my 8 rear-end upgrades with a 3.55:1 possi trac. for my 65 Mustang. It was a complete overhaul, all bearings and seals were allegedly replaced with new ones. I spent a little bit over 1000 dollars for this upgrade. The brand of the ring and pinion and possitrack is Auburn brand.
However, I was pretty dissapointed because this rear end rears make noise opon acceleration. Most noticable after about 35-40 MPH and above . The noise disappears open disangagement of acceleration. I returned to the mechanic Performance Differentail in city of Ontario California, and he stated that such noise was normal especially on 3:55:1 gears. Is this normal?
I can't really stand this noise. It is embarassing because my passengers always ask me "what is that noise" "what's wrong with your car" "are you sure we won't get stranded?",. And I paid exactaly $ 1057.93 According to him it is normal. I would like to know if any of you guys that have upgraded your rear end with same appication have the same problem as I do? What can I do to eliminate this noise. I am know considering on going back to my 2:70:1 non possitrac, to get rid of this embarassing noise.