I remember a friend having a problem with a squeak his XJ and we finally narrowed it down to the CV on the rear drive shaft. The ball on the inside was worn .
We rebuilt the CV and squeak went away
You should be able to test this by
Placing the jeep in 4wd
remove the rear drive shaft ( make sure to place a rag or something in the end of the transfer case , This way the fluid doesn't come out )
Then take it for a spin to see if the squeak is gone .
remember you will not be able to turn as tightly on dry pavement with just using the front wheels
Oh this is also good to know if you are on the trail and break a drive shaft
2005 Jeep Grand Cherokee , 5.7 hemi,Blistein HD shocks and struts
, Eibach pro-kit , 20" SRT Reps, Nitto NT420s 275-55-20 tires, AFE stage 2 dry cold air kit Billet Technology catch can
, Imatation leather disco steering wheel cover
..... more to come