The brakes have been changed on this car. I don't hear the same sound while braking or when the car is slowing down. The sound is only present while accelerating and as the car passes certain speeds... so I assume that it when the transmission is shifting.
On a side note, this car is VERY loud on a cold start. But when started later after a short drive (when the engine is warm), the start up is not very loud. I've had several other cars (not Subaru) and never experienced the same level of noise at a cold start.