Wheel bearing problem?
 

I'm getting rotating noise while driving(like you are on airplane), specially on highway, sounds like it was coming from rear of my car, the frequency increases with my speed, I guessed it was my tyres and rotated them days ago but rear noise persists, Next thought is wheel bearings, what do you think??

Mine is similar to this guy's

if it didn't move with the tires, then bearing is probably it.

if you wanted to cross the T's you might put it in the air and see if you can feel any play/noise in the wheel. we changed a bad bearing in the race car last time, and play was acceptable, but it felt rough turning it

for instance mine makes a noise too, but the front bearings are tight and spin easily, so need to check the rear, but i'm leaning toward a tire

Bearing noise will vary slightly if you load and unload one side or another by turning left and right while driving. If the noise is constant then there are the 2 pinion bearings in the differential and the 2 carrier bearings.

Is your differential leaking fluid or wet oily looking?