Tires: Hummimg from rear passenger side

Question
I have this some what high pitch humming from the rear pass,side I have had my mechanic look at it. he's first thought was pinion gear but when he looked at it, it didn't look too bad so he thought maybe the transfer case but that was ok to. so with a bit of off center wear he replaced gears in the rear, abut the noise remained so at no additional charge he replaced the passenger side axle but the noise remains. My thoughts are a broken or probable loose belt in the rear tire am I crazy or not the rear end does not seamy or vibrate like a broken belt would on the front tire?

Answer
Chuck,

The easy diagnostic tool would be to rotate the tires.  If the noise moves, then it is the tires - and if it doesn't, it is not the tires.

Second, I don't think you mean "broken belt".  That term doesn't have any meaning within the tire industry even though it is used quite a bit by non-experts.  The term is used where "tread separation" is a better term. - and, No, a tread separation would give more of a vibration than a noise.

More likely would be irregular wear (which is another place where the term "broken belt" is used incorrectly), and that is mostly caused by mis-alignment and that would occur on front positions, not solid rear axles (unless the rear axle had a serious problem.)   

So do the rotation and see if the problem is in the tires or in the vehicle.