Prius (2004-09) :: 2005 - Strange Whirring Noise

I have a 2005 Prius with 218,000 miles. Over the past month or two it's started making a horrible noise, which has finally gotten to the point that I can barely stand driving it. I used to keep my radio around 25 or so, but now need to crank it to twice that to hear anything. I can't tell what it is - it sounds vaguely like wheel bearings, but somehow different. The front bearings and a trans drain/fill was done by an independent shop 6,000 miles ago. That shop says the noise is the transmission and definitely not the bearings. My Toyota dealer says the noise is the bearings and definitely not the transmission.

Here are two videos I took this afternoon, which seem to more or less capture it, though it does sound a bit different recorded on a phone than in the cabin:

(this one has a clearer example of the noise)

Background:

I didn't have any complaints with the car until just before the 200,000 mile service was due, when I started hearing front bearing noise (I've had bearings done in about 5 vehicles, so it sounded pretty obvious to me). I brought it to the dealer and was quoted an outrageous amount for front hub assemblies (they told me they couldn't do the bearings, only the whole hub assembly), sway bar end links, alignment, transmission flush, tire rotation and the engine top end service.

I got a much better quote from my local mechanic who I've used for about 3 years, so I had him do the work. This was back in June, at 212,417. He said that they'd never done the flush on a Prius transmission before, but they had the shop manual and were sure of the procedure, and that their Valvoline rep confirmed the correct fluid, and gave them a written warranty in case of any problems. He did note that "a fair amount of metal shavings came out with the old fluid" when they did a drain and fill (not a flush). He also told me that the tires were worn unevenly so I could expect a bit of road noise after the rotation and re-alignment. They an oil change, sway bar end links, front bearings, tire rotation, alignment and reans drain and fill with Valvoline Max ATF, "Toyota Type WS fluid spec." He told me the same thing about the front hubs being complete assemblies, and the part he listed (PBR930641) appears to agree with that.