Acceleration Rumble from the rear?

[Jasonredwood]

I get a rumble sound from the rear when accelerating from 0-40 or so. I think its from the rear? Not 100% on that, but it does seem more rear than from under me. The transmission got new fluids and a external cooler when I bought it about a year ago. Im thinking it could be a U-joint on the drive shaft?

Any suggestions?

Oh and I do get a slight vibration on the freeway but I think thats do to not balancing after lifting the 4runner.