Wierd low-pitched moan in reverse?

This has just started happening recently, and i'll try my best to describe it.

Every time i reverse when my jeep isn't warmed, as soon as i hit the brakes i get this low-pitched noise, almost like a really low goose honk.........

Noise stops when the jeep stops, and it never does it in forward gears.

I just replaced the axle u-joints yesterday, ZJ discs have been on for a few thousand miles, driveshaft u-joints are good, tranny mount seems good as well (no rubber cracks or movement)......'01 xj, 77k

Any ideas?? i couldn't find anything in search

Manual or Auto Transmission? 4WD or 2WD.

The rear drum shoes shift when applying the brakes in reverse, they shift back when applying the brakes while going forward. (Thats how the automatic self-adjusters work, if there is too much slop in the rear drums, they'll shift more when braking in reverse, the shift of the shoes tugs a cable that puts all the self-adjuster gears into motion).

You could manually adjust the rear drums, see if it goes away. Pulling the rear drums may be wise, if you can narrow down the moan more, small pieces can break in the rear drums and cause problems that would make moans.

He has done a disk conversion. Look at his post again. Suonds to me like condensation on the rear disks.

If it is only doing it when it is cold, it would seem to rule out the brakes all together.
Did you swap an entire axle or just brakes?

^just parts, all were new

could this be driveshaft related???

IH8RDS said:

Suonds to me like condensation on the rear disks.

Click to expand...

what makes you think that? just curious...