Easy, I hope.

[Professor Bobo]

I have a hummmmm coming from the back end of my XJ. I'm pretty sure it's coming from the diff. It doesn't make the sound when accellerating or decellerating (foot off gas). Just when cruising at "0 g's" .Like when using cruise control, and your up to speed. Prob a bearing, but which? Carrier? Pinion? Axle? Could it be a u-joint?
Has 8 1/4 rear diff w/3.55ratio
TYIA
Bob

[Osprey413]

I've got the same thing. I haven't really worried about it much though...

[bocaj]

i have same thing to but i only hear it at idle i think its the fuel pump but yours could be sumthin else

[Zoner]

I had the same issue, it was like a driveline vibe but only when there was no push/pull just when engine speed = wheel speed crusing down the highway.

It went away as my rear end began to sag, its gone now. I assume that it was just at the edge of being in the correct angle, and the sag in the rear springs corrected the angle enought that its gone.