We bought our Prius V on October 31, 2011 and only had it three weeks before hearing the groaning noise. Sounded like an old clunker. We also had excessive brake dust at the same time and though that was the problem. They cleaned the dust and it still persisted. We had it taken apart again and cleaned again and still had the noise. We then had the rear brakes replaced and still hear the same noise. We then had the entire rear system taken apart and we still hear the noise. We were assured it was not a safely issue. It used to happen only in the beginning of our journey, but now it is almost all the time. Very loud and frustrating.