[neon_rt]

Sounds like you may have had a lifter that was not pumping up. There is not (that I know of) a safe way to de-sludge the engine if that is the problem. Adding a cleaner to the oil can cause the sludge to start detaching from the engine in pieces and plug something up that is important. That may have been what happened with the noise that you were hearing.
The only solution to the sludge problem that consistantly works, is to use MOBIL 1 or other synthetic oil. I have a friend with a 2000 Intrepid, he has used Mobile 1 since the first oil change and has not had any problem. He now has about 110K miles on the engine. I have never heard of anyone that used synthetic in these engine have a sludge problem or problem associated with sludge. The timing chains are real fragile on these engines, they often break, even when they don't have a sludge problem. The synthetic seems to have enough more friction protection to keep the chain from wearing out. If you have that part of the engine apart, put a new chain on it for good measure. If the chain breaks, the whole engine is toast.