2001 4.0, tick/knock mostly when cold
i'm working on a 2001 grand cherokee 4.0 with 125k miles, and it has a ticking/knocking noise in the engine, mostly when it's cold. it's much less noticeable after the truck has warmed up. it's not overwhelmingly loud like a rod knock, but it doesn't sound like it's coming from the top end either.
i know these questions are very hard to answer over the internet without hearing the truck run, but i'm trying to get an idea of some possible things to look at. when i took it to my mechanic today, it was already warmed up so he had a hard time hearing anything, although he did agree that there was a slight noise. he had his stethoscope out and could not pin point the noise to one area. we took the serp belt off and determined there was no noise in the pullys anywhere. he was thinking maybe a timing chain noise (like too much slack in the chain or something like that), but maybe not since it seems to almost go away when warm. not completely away but enough that you probably wouldn't notice it.
a few days ago i ran some gunk motor flush through the engine and changed the oil to penzoil platinum synthetic because it is supposed to have more detergents in the oil than most other oils, so hopefully this will help clean out the engine a bit if any of the passageways are clogged. it still had the same noise on a cold start and after warming up after doing the flush and changing the oil though.
so, keeping in mind that the noise quiets down a lot once the engine has warmed up, what are some things we should be looking at here? are there any TSB's on this issue?