2007 odyssey "humming"

I've got a 07 odyssey, with 60K miles.
A couple weeks ago, wile driving on the highway, it started to "hum".
I assumed that it was the tires, sense the "hum" seemed to be speed sensative (speed up = hum gets louder, slow down = hum gets softer, slow below 35-40 mph = hum goes away).
So, I had the tires checked, rotated, and had the alignment checked. The alignment was out a little bit on the rear, so I had that fixed as well. And the tires all checked out fine (getting a little worn, but have enough tread left to get through the winter).

Well, the "hum" is still there, so I did a little searching, and found that some odyssey's have had wheel bearing problems, which leads me to my question;
Is it possible for the wheel bearings to be bad, and causing this "hum", even though there is no detectable play in the wheels?

I'm used to being able to check wheel bearings by jacking up the front, and trying to shake the tire, or placing a bar under the tire and lifting, and both of those methods showed no signs of movement in the wheel bearings.

Also, if it is the wheel bearings, would those be covered under the power train warranty, or am I going to have to pay for those out of pocket?

A bearing can be bad even though there is no play, especially the fronts. Drive at a speed where the "hum" is present and swerve left to right. The noise should fade in and out as you loud and unload the bad bearing. When it's a rear wheel bearing going bad we can usually feel the play when the tire is off the ground or just by spinning the tire by hand. If it's a front we usually use a stethoscope to pin point the side. As far as the warranty goes I can't answer that.

Sorry, I forgot to update this.
did the "swerve test", and the hum faded in and out. Took it to the dealer, and they replaced the frotn wheel bearings. Also, just an FYI, front wheel bearings ARE covered under the powertrain warranty. However, rear wheel bearings are NOT.