brake or rearend problem??

I have a '98 XJ. When I begin to slow down and stop with the brake pressed I hear a clunking noise coming from the back. It only makes the noise when the brake is pressed and I am going slower than 15MPH. Also, the time between clunks slows as the vehicle slows. I only have 500 miles left on the warranty and if its a rearend problem I need to know soon. I took it to the dealer today and they said it was just the spare tire "banging" in the back. It definitely was not, but I did not have time to take it back. What does a rearend sound like when it is going bad? The differential fluid, transfer case and u-joints are all ok.
Thanks.

Dealer? factory warranty still or? Anyhow I would get documented on paper for your records of the issues. If it fails out of warranty it would be a + for you in that they neglected to actually inspect it. Also a trip to another shop for inspection with there written diagnosis would be good.

I'm thinking breaks though. My '97 did that until I got the pads replaced. I don't know if the break shop did something else, but I know the noise went away. Just my 0.02

I had a similar noise coming from my '87 XJ during an off-road trip. Everytime I applied the brakes while driving slow the clunk would come from the drivers rear wheel. I was afraid the bearing was bad but after getting home and pulling the rear wheel and brake drum I found the self adjuster frozen from rust and the brake shoes weren't moving to adjust for wear. After busting the adjuster loose and getting the shoes adjusted to touching the inside of the drum the noise went away. If you have rear drums I would look at the brakes.