XJ Knock/Tap at idle-goes away with rpms

So I bought my 2nd XJ a few weeks ago. It's a 99 with just about 60k miles. Everything runs great...excellent oil pressure, good temp readings for the stock radiator, etc. But I am trying to isolate this noise. It only happens when the Jeep has been running for awhile and is warmed up. Also, I can only hear it with the windows up and the radio off. It's like a tap tap tap noise which sounds like its coming from underneath the driver side floor or maybe a little further up. It does not matter if I'm in park, neutral, or whatever. As soon as I give it any gas, the noise goes away. It is intermittent as well. Sometimes it seems louder than others. Originally, I thought it was the flexplate bolts. Yesterday I took of the inspection cover but for some reason one of the big bolts faces the exhaust so I am unable to pull it completely out. I just slid my wrench up and checked the one visible bolt and it seemed tight. I may try and get to all of them sometime this week. But before I do again, any other ideas? Thanks

2 out of 4 the bolt holes on the inspection cover have an open slot so that you dont have to remove the exhaust.

What do you mean they have an open slot? And what is the easiest way to turn the motor to get to all the bolts?

flat tappet cam, lack of zinc/zddp etc etc

jamesonw23 said:

What do you mean they have an open slot? And what is the easiest way to turn the motor to get to all the bolts?

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all you have to do is loosen the bolt that wont come out all the way and the cover will come off. turn the crankshaft by turning the harmonic balancer bolt as if you're tightening the bolt. a helping hand helps but it can be done by one person.

eflores said:

flat tappet cam, lack of zinc/zddp etc etc

Click to expand...

:laugh::rof:

OP: Check all your motor mounts, tranny mount, and the transfer case shift linkage for any play.

Flat-tappet cam. I had drivetrain noise at about 70k. Had been running 5w30. 10w30 and it went away for a solid 100k miles.

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