Hello everyone I'm helping a buddy out with 01 Cherokee. It developed a weird engine noise after having ran seafoam through the oil for 2000 miles and then doing an oil change. It sounds like some kind of slap.

Any ideas where to start would be appreciated

We removed the serp belt and the noise is still there so it's not accessories

Sounds like a noisy lifter to me. Doesn't sound like marbles in the crankcase or a lower end knock. Jeep 4.0's and some other engines are notorious for lifter clatter. You can try different oil to see if it will quiet it down, you can change the lifters (requires pulling the head), or you can live with it.

Thanks for the answer. We've got the valve cover off and think it's something in the 2nd cylinder closest to the firewall

I am one of the other buddies working on this jeep and we found its coming from the bottom end. Possibly spun bearing or a rod broke. How easy is it to lower the oil pan on these?

The oil pan isn't difficult provided you get the front suspension in just the right place. Jack up the front partway, then adjust the height to get the pan out...

I know that noise. I'll bet you're going to find piston skirt in the oil pan.