I had a simular problem on my XJ. It is an 87. I had that noise for quite a few months, and even the dealer couldn't find it. My son Jared was taking a auto mechanic class in College, and I donated my Jeep XJ for a week for them to trouble shoot. They found the problem, it was the track bar mounting plate that is bolted to the unibody. It was just loose enough to allow the bracket to move across the bolts popping against the unibody. Believe it or not, that is what it was. It moved ever so little that it made it hard to see. What they did is put chalk dust on the mount and then turn the steering wheel. When it popped, you could see the dust blow. But I suggest that you use a very good impact wrench, for the first time it was tightened, it did not last very long and it was doing it again. We used a very good impact wrench the second time, and I haven't had that problem since, and that was over a year ago. Like I said above, it will look like everything is perfectly OK by looking at it, but don't over look tightening it for that reason. Hope this helps,
Casper
