I've got a '94 Z28, and once I hit about 90-95+mph, there is a really loud and intense viberation coming from the rear. Can someone tell me what that might be?

 

Edit:
nevermind.. i mis-read the post.

 

i was gonna say it could be out of line, but that doesn't explain loud vibration.your wheel bearings could also be going bad, but you usually hear that all the time nomatter the speed.i wouldn't drive that fast until i had it checked at least.

 

i know this is a long shot but your rotors could be off slighty off balance?

 

Could be an out of balance condition, bent drive shaft, bad U joints, worn out wheel bearings, bad tires, etc.. Whatever it is, I suggest you slow down till you fix it.

 

I would consider looking insid the rear end. Carrier and pinion bearings give off that exact symtom when they go out. I've pulled bad bearings out of factory built rearends with only 50 to 60k on them. It's more common now than it used to be. Bearings are not the quality they were 20 yrs ago. about 80% of the rearend jobs I do are bearing failures.