FYI, post questions like this in the OEM forum next time. This is not a question pertaining to a modified XJ.
The squeaking is coming from your serpintine belt. It's the big long belt that runs all over the front of the engine. Check the underside for cracking and then tighten it. You could probably do it yourself, go get a Chilton's manual and it will walk you through it. Otherwise, a shop will probably do it for next to nothing.
Hope that helps.