First off, this happens whether the Jeep is hot or cold. Second, it doesn't seem to happen in neutral, I have made the noise in both drive and reverse. Third, it's not the transfer case linkage. Fourth, I checked my flex plate bolts earlier this year any they were tight, and it doesn't make a knock like those do.

Under normal acceleration under 2k I don't seem to hear it, it's only when I start to accelerate above 2k RPM.

It's a very light and fast rattle/tick, but it does seems to match engine speed. Haven't seen any side effects because of it. (Transmission shifts fine)

If I could *best* describe it, I would say it sounds like lifter tick (in both sound and how it varies with engine speed) but it's coming from underneath me and only in drive gears.

I'm stumped, any ideas?

 

Have you been able to figure it out? This just happened to me last night

 

I think its a crack in the exhaust manifold. All signs point to that.

Could smell some exhaust in the engine bay on startup.

Going to fix it in the spring.

 

I know this thread is years old but if you happen to see this, my 2000 xj is doing the exact same thing. Did you ever figure out the issue?

 

IDK about yours, but mine has CA emissions with the 2 cats after the manifold. After them, the 2 pipes join and there is a flange with a gasket. Chances are that gasket is leaking or the bolts are loose. Check it out!
It should be right under your feet.

 

check your flexplate bolts, motor and trans mounts, and where the exhaust goes over the crossmember.

https://www.cherokeeforum.com/f51/ho...ocking-125547/

 

I would certainly look closely for a small exhaust leak, broken bolt. Black soot would be a indicator for sure. Under engine back pressure it comes alive.

 

Ooooh! Maybe a plugged muffler or secondary cat?