rubbing sound and feel from 2002 mountaineer

[2000blackxlt]

2002 mercury mountaineer AWD, 152000 miles, hear and feel what sounds like tires rubbing at random speeds, going straight, no acceleration, no braking. The rear brakes and rotors do need replaced per dealer, which is causing rear noise, but today I felt what appears to be random rubbing noises from under the vehicle. Examined all 4 wheel wells and did not see any visible signs of rubbing on the tires, except maybe for the right front. There is about an inch of clearance on the inside top front tire and part of the suspension. I assume that is normal, since it's on both sides. But the rubbing noise sounds like it's under and behind the vehicle. The rear axle needs to be topped off per the dealer, but hasn't in a while. Any ideas before we take it to a repair shop? Thanks!

 

[2000blackxlt]

dealer diagnosed

dealer said I need a rear differential overhaul. $$$$$$$ Apparently they hooked up a stethescope (sp) and heard rattling, etc. in the rear differential. The truck runs fine except for the intermittent vibration/rubbing noise & feel at 50 mph. Ugh. more $$ out of pocket.