Hello fellow Jeepers - I need your help.
The classic 4.0 engine noise is going to put me in a mental hospital if I can't get it resolved
2000 Jeep Grand Cherokee WJ 4.0 in very good shape - I have what sounds like a valve noise but is not constant nor does it remain true to the RPM ( changes intermittent with different rpm and even goes away above 2200 )
What's been done so far :
New lifters installed - new push rods - intake exhaust manifold gasket - head gasket - oil change - flush - cleaned throttle body and AIC valve - checked flex plate - and a few simple things. It really sounds more like a vibration but does increase in frequency with acceleration. I've put a stethoscope under the engine and the majority of the noise can be heard when I make contact with the exhaust pipe just after the split that separates the six cylinders , causing me to think .... Valve train and probably exhaust valve.
I've heard rumors that a CCv and or pcv valve can cause this type of noise. I know the bottom of the engine is in great shape ( wrist pins Pistons main etc ) so I'm good there. Sometimes you hear it well and sometimes it's almost gone. I'm just looking for ANY possibilities from the guys ( or gals ) that have had this type of PITA before and could help me locate the noise before I drive it into the drink. I'm at your mercy my friends - HELP PLEASE

 

Mine was making funny noises and it was the guts in the cat. were loose and rattling around.

 

Yeah, I'd put my money on the cat. The classic valve noise should disappear above an idle, especially with new lifters.

 

Hi fellows, i used to have that anoying noise in my XJ, and it was a piston noise, i had to put a set of new pistons in it and the noise went away....that was my experience, hopefully you don´t need to do this, good luck and cheers!!