2001 XJ 204k miles...rod knock, piston slap, something else?

[njones]

This started a few days ago. Turned on my Jeep, and the best way to explain the sound is if you've ever run over leaves with a lawnmower, the sound was similar to when the mower sucks the leaves up. It was very brief and didn't linger. When I shifted into drive, I heard a loud tapping noise as I accelerated. The most similar sound I can compare it to is the clicking as you climb the first hill of a roller coaster.

In the last few days of driving, I've made some observations about the noise. Whether the engine is hot or cold, the noise is equally loud. When I get into higher gears, it fades significantly. When I decelerate, the sound noticeably fades. It never goes away though. I even hear it at idle. I also checked the oil, and it's clean, no metal or discoloration. I've also noticed there has been absolutely no change in oil pressure.

So far, the only things I've done to see if the noise would quiet at all is adding seafoam to the crankcase, and rying higher octane gas. Neither has done a thing.

Is this more likely to be rod knock, piston slap, or something else? Is there any way to reduce the noise? It's really annoying.

[JPNinPA]

Mechanic stethoscope to locate noise. It could be all you note and include valves, lifter, rockers oilpump drive…
To check for a piston skirt crack you need to drop the oil pan.

Never look down on anyone unless you are helping them up - Jesse Jackson

[Houdini]

Also concider a flexplate crack if an automatic. It can sound similar. FYI, premium fuel will not make a difference. Your engine is designed to use regular and premium is a waste of money.

[superj]

Also, this has happened to me on two different cherokees, the bolts holding torque converter to the flywheel had backed out a little and were hitting