Yeah, its really nothing to worry about. It's really just a flaw in design of the motor. I would be willing to be that any Jeep you see on the road or a used car lot probably has the same knocking noise. I doubt what you hear now will really ever get worse, the rings will probably wear before anything else happens. The 4.0L is just based on an old design, when you keep adding new technology to an old design you have some minor problems sometimes.