I'd like to know if you figured it out OP. I have the same issue, no matter what gear mine is in. I even get it up to 100+ then pop the tranny into neural and it still does it. I've heard it could be the pinion flange if its worn really bad?
Yes the issue is still there, but I don't drive the car it just sits in garage. Needs plates, I need adjustable uppers to set the pinion angle everything else is new