I have the same chirping noise in my 96 XJ. I am still diagnosing, but I jacked up each side of the front end and had a friend rotate each wheel. Still had the squeak. I think I can hear the noise coming from either the double cardon joint near the transfer case or the transfer case itself. This weekend, I plan on taking out the front driveshaft and repeating this. If the noise is gone when I rotate each wheel, I will know for sure that it is not in the pinion bearing in the front end. Then I will drive it with the front shaft out and in 4WD to determine if it is the universal joint or something in the transfer case. Where did you get your joint parts? Keep me posted on your investigation - may save me some time.