Jeep engines are noisy by nature, so maybe nothing is wong. But it could be a valve or lifer, or the timing chain that is stretched. You can try replacing a quart of oil with a quart of ATF; I have heard it helps (never tried it myself, though), as well as some aditives that have cleaning agents... If you replace the timing chain, dont forget to replace the tensioner as well... And keep in mind that (at least on the 2.5L) you need to take out the belt, fan, pulley, timing chain cover and oil pan to be able to replace the thing (it's easy, but it takes some time to do and you will need the puller to get thepulley out).