[Fen335i]

I have a sound that is somewhat intermittent, but does seem to present itself almost every time I drive the M. Its a low grinding/rubbing sound that is most evident at lower speeds, but it can be heard at higher speeds too if you listen carefully. it sounds like its coming from the passenger side of the car, and I think its specifically the rear wheel. It almost sounds like the brake pad is rubbing up against the rotor. Kind of a brushing noise...definitely not normal. Anyone else dealt with this? I took off the wheel and inspected both passenger side brakes, but didn't see anything unusual. Could this be a bad caliper stuck and not releasing like its supposed to? Or, maybe an emergency brake problem? Any help would be appreciated. The only other thing I can think of is a bad wheel bearing, but at 44,000 miles that would be far too early for a wheel bearing going bad.