Is this your first Jeep? 2.5L's as well as 4.0L and 4.2L's have noisy valves. It should die down a bit once the oil pressure is up. Although an exhaust leak could be a possibility as well. The rear most exhaust manifold stud tends to break off causing a leak.
If you know how to check the valves then it wouldn't be that big of a deal to do with only 16 valves to check. Although it should have been checked when it was rebuilt. 6000 miles is nothing.
