Well I've done all the maintamce on my XJ. Recently did new lifters water pump, thermostat, and more. Drove the jeep to Home Depot came back. Drove like normal. Get home and start it back up to leave again and this noise!!! Should like motor if about to blow. A loud clunking noise. I took off the valve cover and checked that all rockers/lifters seem to be working fine. Leads me to believe bearing?? It's not the flex plate.

http://youtu.be/QfpDxZloVsA

 

Did you open the hood to see where the noise is coming from? It's kind of hard to tell but it sounds like an exhaust leak? Maybe a cracked exhaust manifold?

 

Sounds like metal to metal grinding?

 

First question: why did you change your lifters? That's not routine maintenance. Did you have an issue before that? It is hard to tell where the noise is coming from. Get an automotive stethoscope and find out. My initial thought is that it's under the valve cover where you just messed with things. Eliminate the on opus things first.

 

The reason why I did a lifter change a few months back, is because I had the dreaded lifter tick. Once I did that the jeep ran fine. I opened up the valve cover and everything seems to be normal in there. I would have to agree it does sound like metal on metal but cannot find it for the life of me

 

Missing spark plug.

 

I took off one wire at a time and nothing. Oil pressure is great and doesn't feel like I'm loosing any power

 

Something you could try is to probe with a long screwdriver and put your ear on the handle end. This acts much like the automotive stethoscope. You can hear a lot of things inside the motor this way. Find the loudest area and you may get an idea what is going on. Best of luck.

 

Sounds like the pistons are swapping holes.