I recently purchased a new 2006 WRX and have driven about 5k miles. Since the day I purchased this vehicle, I have noticed that the brakes make a humming noise when applying moderate braking pressure when the vehicle is moving faster than 40 MPH. The humming will stop when the vehicle goes below this speed. There is no pulsation in the brake pedal and it does not appear to affect braking performance. It seems like the sound comes from the rear brakes, but it is difficult to tell since the sound resonates in the whole vehicle.

Is this a normal noise for this vehicle? Would sanding the brake pads and re-bedding them solve my problem? Since the vehicle is under warranty I could take it to the dealer, but I am concerned that they will simply grind the rotors. From what I have read on this forum and on NASIOC, milling the rotors does not seem to be a good long-term solution.

Thanks in advance for your help!