Bad rear wheel bearing?

I've got an 03 tundra 4wd 4.7l that makes an awful droning noise when it gets up to speed. Sounds like you're in a helicopter when on the interstate..
I had one of the front wheel hub assemblies replaced by mechanic and did not fix the issue, he said the other bearing/assemblies were okay. I tried jacking up the truck and checking myself and when spinning the wheels by hand the front ones feel and sound fine, can only hear the light sliding sound from the brake pads, but both rear wheels feel and sound very rough, not smooth at all. however, when I check for play or noise when shaking the tire side to side or up and down it has no play and makes no noises. So I raised up the rear axle off the ground and put it into drive to let the rear wheels spin freely, it makes a very rough grinding sound when I do this that gets louder the faster the wheels spin. It sounds like the noise is coming from the wheel on both the right and left side and not from the middle of the axle. Does this confirm bad wheel bearings?

 

The first thing to do is check and see if you have the correct amount of fluid in the read differential. Normally you'll see evidence of leakage on and around the rear wheels and brake drums. Make sure you cover the basics first before going down the road of rear bearings. Check the rear brakes as well.

 

So your mechanic can't locate the bearing noise??

 

I missed this. Might be time to look for another mechanic. Good catch @KNABORES .