Sorry to drag this one up from the dead, but I am curious to know what you (Sine Deviance) ended up doing with this.
Thanks.
No problem. Believe it or not, the noise wasn't coming from the engine at all. It SOUNDED like pinging or valvetrain rattle, but it was actually the dust cover that bolts onto the bellhousing. I'll explain. Before I started having this problem I replaced my clutch. After driving it for a while the noise started. It had been at least a couple weeks since the clutch so I didn't think they were related.
After this thread, one day I started getting some very bad vibration when pulling out in first gear. I instantly thought "transmission is loose!" so I decided to crawl up under the Jeep and check the bellhousing bolts to make sure everything was still tight. They weren't. There were two or three bolts that had somehow managed to work their way loose, and a few of the bolts for the dust cover somehow got broken and fell out. The dust cover was only being held by one bolt and the transmission wasn't bolted up tight, so the dust cover was basically flapping in the wind at this point. That was where the sound was coming from.
I held up the dust cover and tightened all the bellhousing bolts. The sound went away and hasn't been seen since