I find mine only does it when cold. I tried a few things people suggested (different oil viscosities, synthetic oil, oil filter) and nothing has worked. A few people I have talked to at the dealership have the same problem and have tried the same solutions all to no avail.

What weight of oil did you use?

Well, Changing the oil filter didn't fix mine. I went out and started it today(been sitting for 3 days) and Knock, knock, knock, it was back again. It goes away almost immediately after start up. Sounds like a dry start knock for sure but not sure why.( I thought it had to be the oil filter draining over time)

I only have 1500 miles on it and it only knocks after it sits for a few days.

I keep it inside a heated garage that might get down to 45 at the coldest so I know its not just cold temps.

Do you think I have a problem with this engine already? It runs fine after started and never knocks if I drive it daily. Do you think this could be a bad antidrain back valve problem on the oil filter? I have a mobil 1 filter on it now.

Mine and a few of these other guys only do it when the engine sits a while... did your exhause manifold problem only knock when cold as well?

I have a 2007 with 24000+ miles on the almost year old engine. I have experienced the same knock upon a cold start up. I have found that by using either what ever the Jeep dealer uses for oil or what I have changed to, Mobile 1, the problem seems to almost go away. Every now an then I will hear a faint knock but it is defiantly not as noticeable as with the other quick lube type oil that I have used a few times.

Mike

Knock Knock
 

FYI, the larger capacity oil filter from MOPAR some people are using will for sure cause knocking, beware !!!!!!!!!, the larger filters internals are very different then the spec MOPAR filter, thus the drainback pressure valve is set different.

Mine has always done it if its left for more than 12 hours. I had a brain fart and thought it might be cause by a hydraulic lifter bleeding down. Goes away after a few seconds and some new oil pumped into the lifter???? Are they even hydro lifters in the 3.8?