2008 Dodge Caliber Noise

We had new tires placed on the car about 7,000 miles ago. No sounds and smooth driving until fairly recently when the back tires seemed to be making a loud humming type noise when going down the road, that would increase with speed and decrease as you slow down.

We had the tires rotated thinking it maybe something with the tires, this did not solve the noise. It was also time for the brake pads to be replaced and thought perhaps the noise was coming from the pads/rotors. We replaced all four brake pads and the rotors. The noise is still there. The mechanic checked everything, suspension, shocks, all were good. He stated it could be possiibly noise coming from the wheel hub itself.

Trying to determine iwhat other possibilities this could be? New tires, new brakes and rotors and we still have this noise!