My 2004 Prius (90k miles) recently started making a low rumbling noise that seems to emanate from the front passenger wheel area. When I took it to the dealer they replaced that wheel's bearings, but the noise persists. The noise is not present when driving on very smooth patches of road, but the slightest bumps will trigger it, and it is independent of vehicle speed or wheel direction. (It is harder to hear at high speeds due to general road and wind noise, but it is definitely still there, and at about the same sound level.) It does not sound louder or any easier to hear when I stick my head out the passenger window, leading me to believe the source of the noise is internal of the wheel well. I've inspected as best I can the region in and behind the wheel well for loose parts, but everything seems fine. From my reading of other posts, this sounds like it could be a problem with the transaxle. Does that seem like a reasonable conclusion? If so, what do you recommend I ask the dealer to do to test that hypothesis and/or fix the problem?