Weird rear end noise

[M1911A1]

Please Help! I have been having a weird (to me) condition with my 04 V8 4WD. with limited slip, towing pck. After about 25-30 miles of highway driving starts making a rubbing noise at about 5 or 6 feet of pavement trajectory.
The noise sounds as if a caliper was warped, or some braking component would be binding, but I checked the brakes and are fine. Also turn the wheels by hand and no noises or friction. In the process of checking replaced a rear wheel bearing that was beginning to show lateral play on the wheel, although wasn't noisy yet. Could it be the rear differential? I replaced the fluid with 75/140 synthetic and a tube of friction modifier; the old fluid was clean! Please Help.

 

[TechGuru]

starts making a rubbing noise at about 5 or 6 feet of pavement trajectory.

What does this mean exactly? While turning?

If you only hear it while turning I would think you're hearing your LSD clutches rubbing.

 

[M1911A1]

Driving in any direction, doesn't matter if I turn or not. As a matter of fact when I noticed play on one of the rear wheels, took the car to a parking lot, and made some eights around, and didn't notice any difference in the rubbing sound; but decided to replace the LR bearing on account of loose play on the wheel. The thing is that when I start driving the car is perfect until driving for at least half an hour, and then you hear this rubbing noise from the rear, speed dependent and about each 5ft. of distance traveled.

 

[roush9799]

Did you check the parking brake shoes also? Mine were in pieces last time I had it apart. Had the same thing happen on an f-150 once, and it made a rubbing noise at times.