Rear Noise ARGHH

Whats up, I've done alot of searching on stangnet and I'm under the impression it may be worn U Joints, or something to do with my Wheels, Or Axle Bearings? I'm not sure .

Anyway Its a sound that occurs around 15mph+.. It's a "RRRRrrrrRRRRrrrrRRRR" noise that kind of sounds like I can hear my tires rotating.. It gets a little louder and faster as I go faster. It can be heard more on the drivers side and it's been Buggin the hell out of me lately.. I have 295*50*15's on 15x8 welds with a 31spline 8.8 Rear with 3:55's, No Quads, Lakewood 50/50's, MAX MS Adjustable LCA's.. No Tailpipes (So I can rule out the tires rubbing on that) When I bought the car with 255's on a 16x8 wheel with tailpipes it was making that sound.. and I was told it was the tires rubbin on the tailpipes.. (Obviously it wasn't that now) It can kind of be felt in the floor also.No Problems with Performance at all.. just that dumb sound and a little Vibration... Lastly I've replaced the rear end fluid about a month ago and checked the gears, Gears looked fresh from what I can see, no scoring, everything looked alright in there. Also there is no sound deadening in the car (which I would be assuming maybe that's why I can hear it louder than if I had the sound deadening in my ride?)

Anyway I am bringing the car to a friend's shop to put front struts in and will have it on a lift so any Ideas on what it can be and how/what to check while it's up there will be appreciated...
Thanks

yeah, the car came with the 3:55's so I am going to have to findout what brand the gears are.. Like I said it sounds like a Tire rotating...kinda like a Thump thump more... "thumpTHUMPthumpTHUMP" like tires rotating around.. hard to describe