Volvo Repair: 2004 Volvo XC70 Rear Humming Sound, 2004 volvo xc70, volvo xc70

Question
I purchased a 2004 XC70 2 weeks ago with 70k miles.  Unfortunately, I noticed the day after that there was a humming sound coming from the rear end of the car.  Took it back to the dealer where they looked at the wheel bearings and said it was not that.  The dealership ended up replacing one of the tires b/c they thought the metal belt in the tire was loose.  Did not fix the problem.  I then went and changed all 4 tires from Pirelli (as I heard tread noise is a problem) to BF Goodrich Traction TR's.  This did not fix the problem either.  There is no vibration or pulling on the car.  It also does not make more of a noise when turning.  It currently sounds like the car has a flat tire coming from the passenger rear side of the car that is most noticeable on flat roads from 5-45mph (higher mph masks the noise) and the sound seems to be getting louder.  Any thoughts?  We are preparing to go fight with the dealership but it would be nice to have some idea of what might be wrong.

Thanks,
Sara

Answer
A check of the wheel alignment may provide some answers. An out of alignment situation can cause tires to scrub and make noise. Hard to say if thats your problem from here though. Rear brakes make some noise, possible seized parking brake cable could be hanging up the parking brake shoes. Caliper could be sticking.Exhaust rattle or vibration from broken hanger...Loose inner tailgate panel...?