Odd 4.0L Cold Start Noise

Hey guys -

Hate that this is my first post here, but I thought I would reach out to the experts. Plan to take the Jeep to my local mechanic in the next few days, but wanted to see if any of you guys have experienced this noise.

For some background, I found this 06 unlimited about 4-5 months ago. Had been searching for one for a long time. She has the six speed manual tranny and had 46k miles on her. Pretty rare. I can post more about her later.

Noise started up late last week. Only occurs on cold start after about 30 seconds. Usually lasts for about a minute. After that I get a tapping from farther back in the head for another probably 3-4 minutes until the engine is fully warm. Then it goes away and doesn't return until the engine is fully cold again.

The only think I can liken the sound to is a turkey call, lol.

Here is the video. Noise starts around the 0:40 mark and lasts for about a minute. Tapping starts after that.


Any thoughts?

Steel City 06 said:

Has the Oil Pump Drive Assembly (OPDA) been replaced?
Mine sounded similar to that when cold, (but without the warbling) and it’s a very common issue in 05-06 TJs

Click to expand...

I am not sure. So that means probably not would be my guess. What does that involve? DIY project or leave to the pros? I will do some research.

Thanks for you good responses guys. On watching some other videos, this looks to be the same sound/issue. Went ahead and ordered up the Crown replacement unit this afternoon.

Now for the fun part, the pictures!

First day when I brought her home:


Interior is immaculate, which it should be for a 46k 06 Unlimited:


Same goes for the engine compartment:


Sorry for those that are partial to chrome and tube bumpers, but those were the first things to go:


Sneaky shot of my 78 Chief in the background....


And the 79 CJ5 with a small cameo, way in the background....


Snagged a Warn RockCrawler Tire Carrier for cheap off Craigslist:



PO had put on the 3.5" RE springs and some ProComp ES 3000 shocks, along with a rear track bar relocation bracket, and extended front sway bar links.

I knew this wouldn't do (not done the right way), so since then here is the list of what I have done (so far):

Rokmen Fully Adjustable Control Arms
Rancho RS9000XLs
Novak SYE and locally built rear DS
Novak 231 transfer case linkage
All new fluids, plugs, filter etc.
Buchanan Precision 1" Seat Risers (game changer)
RockHard front bumper
Warn VR8
RockKrawler Rock Guards
Warn RockCrawler Rear Tire Carrier

Left to do:
JKS Front and Rear trackbars
Walker Evans 501s
New 33x12.50s (Milestar Patagonias or another set of BFGs)
Drive the heck out of it

Well you guys hit the nail on the head. Mechanic put his stethoscope to work yesterday morning and he confirmed the ODPA is definitely the culprit. Swapping in the crown replacement. Only bad part is the cam sensor was basically seized in the housing. He soaked in penetrating fluid all day, but still could not break it free. Wound up breaking off a little bit of the plastic in the attempt as well. So they ordered me a genuine Mopar one to throw in the new ODPA. I will keep the one off the Crown unit in the Jeep as a backup. Thanks for the good advice guys!