99XJ, 4L, AW4, ~170k miles

I've been chasing around an unfortunate sounding engine knocking which is more apparent from the bottom end of the engine/bellhousing area than the top. Jeep starts up quiet, knock gets progressively louder after 10-15 seconds or so after RPMs fall to normal idle, stays pretty noticeable during warm-up, and gets quieter (but doesn't go away) at temp. First thought was flex plate/torque converter bolts - I found those loose ~10 years ago. I've gone so far as to use a 15mm crow foot socket on a torque wrench with a pully holder on the harmonic balancer to make sure that I've got at least the proper 28 ft-lbs of torque on all 4 bolts... they're not moving around. I don't see any obvious motion when gently prying on the flex plate with a long screw driver... but I do see some odd discoloration near the middle of the plate coming from the spacer near the crank.




Anybody else seen this streaking or am I reading too much into it?

My only other guesses are piston slap or rod knock - but I wouldn't expect that to improve with temperature. Oil pressure and performance are all normal... ~50 psi at startup, ~30psi at hot idle... from the dash gauge. Exhaust appears to be leak free and no weird pre-cat exhaust smells. Stethoscope around the block doesn't reveal anything unusual - the sound is always louder without the stethoscope than it is with it. I had the oil pan off about a year ago and no obvious piston skirt issues, etc. I'd rather not just drive it till it breaks to figure out whats wrong... but I'm running out of ideas.

 

Could the flexplate be cracked? https://www.cherokeeforum.com/f51/ch...xplate-172081/