Rear Rubbing Noise Driving me Nuts!!

I know there have been many threads about noises in the rear but mine seems to be a little different.

I can hear a low intermittent rubbing/buzzing noise towards the rear of my '01 Cherokee. It won't start until I go over a large bump or dip but then it becomes sensitive whenever I go over the smallest unsmooth surface. It's not constant noise but the pitch and speed of the noise is the same if I go fast or slow, turning or straight, over large or small bumps/dips. I will only hear the sound when it goes over a bump/dip.

If I park it for a while or overnight , I will not hear the sound again until I go over another large bump/dip and then the process starts all over again.

It does not sound like metal on metal but more of low buzzing/humming noise.

Any input would be well appreciated since I am new XJ owner!

When you say pitch and speed stay the same, do you mean that it continues even when stopped? If so, I'd say fuel pump.

Is it a rotational sound or just a magnified rattle/buzz. If so these two suggestions may sound a little far fetched but here goes:

Check you exhaust hanger at the rear end, especially if your Jeep is lifted and you never made adjustments in your pipe against the leaf spring. Mine clanked and bumped until I fixed it. Somehow it made more noise inside the rig that outside and drove me nuts.

If you have a roof rack (stock OR aftermarket) make sure all your connectors are tight, my rack was vibrating like hell but I never even suspected the rack until I grabbed it one day and it was loose. After I tightened it all up the vibration went away, for good.

x2 on the fuel pump.

I just put a new muffler on mine, then it started making nose back there, put it up on the lift friday nite and noticed it was hitting the rear axle, the shiney spot was a dead giveaway. Massaged the pipe a bit after loosening the clamps and it's quiet now. It's amazing what an annoying noise like that can do to you, it sounded much worse than it was.