I appreciate any help you guys can give me on this. I have a 95 GC 4.0 with auto tranny. Two or three months ago I starting getting a noise that sounded like something loose and vibrating either under the dash on just on the other side of the firewall. Sounded like metal on metal. The noise would just happen when the transmission kicked down into passing gear, like when climbing a hill. The past 2-3 weeks I get the noise at other times. With the engine idling in D, it sounds like tick-tick-tick. When I pull away, the noise speeds up and changes in pitch/loudness as the transmission shifts through gears. It seems to go away once the vehicle is up to speed. If I shift into N when stopped, the noise stops. When I put it back into D and pull away, about half of the time the noise is gone and doesn't return until the transmission kicks back down again. I should point out that I only get the noise AFTER the engine is warmed up. I have searched this and other forums and exhaust leak/cracked manifold and lifters are the most often mentioned. My son was passing through the other night and looked at it briefly. He said the noise was definitely coming from the top of the engine, and probably from #6 area. He mentioned injector vs lifter. He said start with injector, as that would be cheaper. I haven't seen any mention of noisy injectors, just decreased performance. This jeep is lifted, and about the time the noise got worse I got steel rockcrawlers and 32x11.50s, so it is straining more on hills. The engine has about 80k on it and the transmission was rebuilt last summer. New oil pump this spring. Oil pressure is fine. Dumb question: will a valve adjustment eliminate a noisy lifter? Any oil additives that can quiet it down? Sorry for the long post.

To me, it sounds like two similar but different noises from your description.
Exhaust leaks generally get less noticeable when warmed up.
Hydraulic lifters can not be adjusted.
I would try an oil additive like STP and see if a little thicker oil will keep the lifter pumped up.
80k isn't a lot of miles for lifters to be going bad, but not out of the question.
It could also be engine knock, or as mentioned a noisy injector.

Thanks, I'll try the STP to see if it makes a difference. How thick can I go on the oil in cold weather?