With the utmost and sincere respect to keith, I recently discovered the hard way that a bad wheel bearing can manifest itself as a grinding sound when braking but only a mellow oscillating growling sound when not braking. Mine just did. And mine was a 2005 Toyota product (a Scion). I also discovered in doing a bit of research that Toyota (and other manufacturers) has switched to double-row ball bearings in the wheel hubs to reduce friction and they're apparently not holding up well over the long haul.
However I'd also like to point out that sound travels, and the sound may not be coming from where you think it is. In my case I changed both front bearings on the theory that their lives were probably fairly similar since they both came from the same gene pool. Problem solved. I plan to do the rear bearings proactively soon.
Your best approach is to
(1) jack up one corner of the car at a time. For the front wheels, apply the parking brake, chock the rear wheels, and put the tranny in neutral. For the rear, take the parking brake off, put the tranny in 1st or reverse, and chock the wheels.
(2) first, try spinning each wheel by hand. Feel and listen for roughness.
(3) after spinning each wheel, remove the wheel and try turning the hub by hand. Sometimes without the wheel damping the vibration you can feel it in the hub. IMHO it's a good way to check the bearings.
And I agree that you should get a new shop.