2003 Honda Odyssey wheel noise?

My Odyssey makes a whining noise that increases in tone with wheel speed - NOT engine RPMs; while rolling, I shifted into neutral and revved the engine - the sound remained constant.

At lower speed (under 30 mph), it almost feels as if something is rubbing or grinding, but as I rotated tires, the rear wheels seemed to spin smoothly. There is no popping or other sounds that might indicate CJ joint trouble.

I suspect either rear bearings or a transmission issue; this van has already had the recall repair done, but I realize as I type this that I have not checked the transmission fluid level.

Opinions?