This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.
We recently bought a 95 Cherokee with the 4.0l 6cyl engine. After a
couple thousand miles, it started making a knocking sound at idle. It
sounds to me like one valve is out of adjustment.
Don Ferrario responded: This is typical of the 4.0L engine. Other than the
sound, which is admittedly alarming, it should not cause any other problem.
(note: In 1996, the 4.0 was redesigned to lower noise.)