04 SR5 humming from rear

Starts humming at around 25mph and gets louder and higher pitched as I accelerate. Noise stops when I turn right so I assumed it was the right rear wheel bearing. I replaced the hub bearing and the noise continues. Also had the tires checked out and they seem to be fine. Anyone else experience something similar? :banghead:

Have you looked at the diff?
Maybe a pinion bearing or something.
Start by checking the gear oil level in it.