One of my 05 Jeep Wranglers was like that with Rotella 15w40 oil. It sounded awful (especially the OPDA on a cold startup) and it preferred 10w40 Mobil1 dino oil. The other Wrangler with the exact same mileage did perfectly fine with the 15w40 Rotella.

 

I 100% believe it could be the oil. I’ve heard Valvoline 20/50 VR1 is really popular as well for these due to the ZDDP levels.

I might switch to 10/40 though and see if it subsides.

 

I scored 10 quarts of Valvoline 10/40 conventional for $.10! No joke.

Now running 10/40.

I paid close attention to the noise this morning and here are my observations:

- More noticeable when the motor is cold

- Once warm it goes away at idle, but is noticeable when shifted into any gear other than Park.

- Oil viscosity did not seem to make a difference, but I do think I’ll be running 10/40 for now. I added the Comp Cams break in additive as well.

 

More information on this sound:

It seems too slow of a tap to be motor related - just my opinion.

- It does get more pronounced in any gear other than Park.

- It is only noticeable from the sides of the car, underneath, or in the drivers or passengers seat.

I cannot hear it from under the hood at all. The motor sounds super smooth from under the hood.

I would describe it as a Gentle Tap.

Here’s more information I neglected to provide:

The PO did a half *** job securing the bellhousing to the motor after pulling the motor to put in motor mounts. I put about 1,200 miles on the truck with two loose bolts securing the bell housing.

As soon as I noticed it, I got more hardware and snugged it up. Hasn’t been as issue since.

After more thought, I realized that it has been making this noise since BEFORE the hydrolocking incident.

 

More info after continuing to monitor:

- It's a tapping sound at probably 120-160 rpm. 2 or 3 taps/ second
- It's not present when the truck is cold (I have an exhaust leaks somewhere that is more prevalent when cold, then goes away with temp)
- I have listened to videos of the slipped liner tapping sound and that's not what it sounds like. Not a fast enough or loud enough tap in my opinion. But, it does have some characteristics of the slipped liner. Only taps when at operating temp and only at idle. Any RPM above idle, even a few hundred RPM, it's not noticeable
- The noise is most obvious when you're directly under the bell housing/ flywheel area. Moving rearward from there it gets quieter, and moving forward from there it gets quieter.
- Still cannot hear it at all with the hood open.

 

My money is on a crack developing on the flex plate but hard to say since I really can’t hear the noise in the video. If the bell housing was loose with the engine that could have put stress on that part and could also make sense that you hear it more when in gear vs in park. Have you tried removing the inspection plate at the bottom of the bell housing to see if you can hear it better? You might be able to see if there are any cracks starting my either removing the rubber plugs on the back of the oil
pan or remove the whole oil pan to get a better look.

 

That seems to make the most sense. I have not pulled off the inspection plate, but that is probably the best next step.

The noise is not easy to hear in real life either, and it's not consistent. It shares nothing in common with the threads I've read about the slipped liner noise, but I've read a few threads about Flex plates and it seems to share a lot in common with those. When it's making the noise, if you raise the RPM at all above idle, it goes away. That seems common on cracked flex plate ticks, whereas cylinder liners, lifters, or other motor noises require more RPM before becoming inaudible.

 

Yep tracking down a cracked flex plate is a PITA. Spraying some kind of lube up there around the center of the flex plate can make the noise change as the lube/spray fills the gaps/cracks in the flex plate.

Only vehicle I've owned that had a cracked flex plate was my 05 Rubicon and while I'd like to blame Jeep for their cheap parts, in this case I blame the Jeep techs that tore my transmission out under 18K to check the transmission as it constantly went into Limp Home Mode. They tore it out, and I believe when they re-installed it bent it or caught it as they were stabbing the engine/trans together. At about 24K on the clock I started hearing a faint tick. Jeeps have a poorly designed manifold to cat connection and they constantly get loose. Well I modified that and while the exhaust no longer leaked I still had a tick. Well fast forward to just as the warranty ran out the sound went from a tick to a knock. I took it to several places and they all said "I dunno" but drive it until it dies, and you'll find out what it is... I was not satisfied with that as a diagnosis lol. However I could not track it down!!! Finally in a Jack in the Box drive thru line enough was enough. It started to cluck like a darn chicken! Here I am in this highly modified tube fender Jeep Rubicon with cargo netting all in the rear, lifted, and ready for anything, but nah it sounds like a 500.00 junk yard vehicle! The guy in front of me stuck his head out the window, then he shut his car off (I had raised the RPM's to silence the clucking chicken sound at that point). He then opens the hood, scratches his head, and goes man did you hear that?? My car is making a weird noise... I didn't wanna dare tell him it was me after all that! I got home and got to work on figuring it out! I left it running as it would not do it cold. It had to be warmed up to cluck. I removed the inspection plate (more like a D1 inspection plate) and I used some WD-40 and sprayed the center of the rear main area. The sound changed and then went away!!! I drove like that for a few days and it was silent. Then it slowly came back, I got creative and used long Qtips and packed the darn area full of Lucas Red & Tacky. The sound was gone for nearly a month. In that time I found out the part was only like 20.00 and it reminded me of a darn pie pan you'd buy at the store for 1.00 if that.

I had no way at the time to drop the TC/Transmission so a local Jeep Club sponsor (Clearlake Jeep) offered to let me take it down to their dealership after hours and one of the club members would help drop the transmission. They highly doubted it was the flex plate and told me they'd help me with a discount if I needed a new 4spd Transmission (which I was going to go back and fight Jeep over as they did an awful job at 18K and even dented and crushed my transmission pan which I myself had to fix...). We were slowly removing the transmission and it made this stupid sound which reminds me of a Snapple Bottle cap sound. To our amazement the entire flex plate was torn completely around the mounting bolts with only 1-2mm of metal holding it together! The dealership was amazed, and they were very satisfied that I had properly diagnosed it lol.

We installed my new pie pan looking flex plate and carefully re-installed everything. For the next 20K before I sold it she was quiet again!! I was very grateful Clearlake Jeep let me do the repairs at their dealership for free. The tech/Jeep club member totally agreed with me that the other dealership that dropped my transmission originally caused the damage to the flex plate.

Sadly that was not the last time I had to drop the Jeep off at the dealer as shortly after that the very expensive cat setup took a dump and caused me to fail my state inspection. It was under the 8/80 Federal Emissions warranty still and Jeep was not happy I dropped it off for a free cat setup at the dealership closer to me (not Clearlake Jeep because it was to far away and Jeep never offered a loaner or even a rental). They tried to tell me it was covered in mud and that my warranty was VOID. I had to get mean and tell them oh you can advertise them driving thru swamps, over mountains, thru rivers, and down muddy trails, but I go and drive the darn thing down my parents 90 acre ranch drive way and my warranty is voided????? They then told me okay we'll cover it, but your Jeep is muddy underneath... I thought to myself you have no idea what a muddy Jeep looks like lol. They then told me oh those cat's are on a nationwide back order, and I'd have to wait 2-3 months. In the mean time I wasted 40.00 on the inspection as I only had a few days to repair it. They called me 2.5 months later and told me they were instock and to drop my Jeep off.

I hit a bayou near my house and my Stone White Rubicon was covered in orange mud/clay/sand. I then rushed home and got out the power washer and totally cleaned the underside of it to looking brand new. I left the body and roof alone and let it completely dry. I then drove to the dealership and wheeled right up to the Service Advisor which had given me so much grief. I hopped out and said NOW THAT IS WHAT YOU CALL A MUDDY JEEP!!!! I said it so loud people from across the lot were looking at me. He was about to say something mean and then I said go ahead and look under it... He got down and looked and just looked at me. I waited in the waiting room for an hour and he came in and said it was ready. He had me go to the cashier to sign, and while I was up there I asked if they did car washes. To which the lady said oh sure hun (she hadn't seen my Jeep haha). My Jeep was brought around, and he handed me the keys like get out of here. I then kindly said oh I'd like it washed please. He turned around truly pissed off and it was gone for 30min. I watched em wash it, and then they spent more time cleaning out the car wash bay lol. After that my mind was totally made up. I got home, told my wife well I am going to remove some stuff off that Jeep, and then sell it. She didn't believe me for one second. Then she saw me tear off $$$$ parts over the weekend sell em on CL, and by the next weekend I sold it!

Don't go and sell your LR lol, but yeah I am starting to think you have a cracked flex plate. It sure sounds like what I experienced.

P.S. Sorry for the long story, but I had to tell how I got back at that dealership lol.

 

Great story @Best4x4. I’ve had three Dodge diesel trucks and have had pretty poor experiences across the board with the dealerships as well. Have also had a JK wrangler. My D1 convinced me to never own another Jeep.

Sounds like the best way forward is to pull the little access port on the bottom of the bell housing and look for cracks.

Im also monitoring the noise, as it’s not consistent and sometimes I just think I’m hearing things. It’s always possible I’m just mistaking it for the sound of, you know, the engine running...

I like to think I’m pretty good with identifying these things as my “day job” is essentially driving, riding in, and teaching others how to drive on race tracks. But being able to make a suspension adjustment doesn’t correlate to identifying a tapping noise I guess haha.

 

Quick update. Truck still has this noise, but it has not changed at all. It’s very subtle still and only at idle when warm. Any rpm above idle, in any gear, and it’s gone.

At this point, I think I’ll just try a different oil viscosity which each change and see if that affects it. My change from 15/40 to 10/40 made no difference. Going to try 20/50 VR1 next.

My trans does shift kinda sloppy. 1st to 2nd is rough and it sometimes can’t decide which gear to be in. I’m not sure if it’s correlated, but the noise does sound like it’s coming from the drivetrain area and not the motor.

The trans fluid was supposedly changed before I bought it, but maybe I should try flushing the trans fluid and changing the filter?