Had some vibration and what sounded like sandpaper rubbing together when I drove the Jeep, even in 2wd. Had some concerns about the noise I was hearing in 4wd back at the Crawl. Took my drive shaft out and the rubbing noise and vibes went away.
Took the shaft to a drive shaft shop this week and they found that the slip joint had come off and been put back on "off camber" meaning the u-joint caps on that joint were not lined up with the caps on the double cardin. They also found one of the u-joints in the double cardin was starting to come apart. I was never aware of the required lining up of caps, and they explained that when they are not lined up the joints cause vibration because they are working against each other.
I had them service the shaft - $45 - to include a new joint, reposition the slip yoke, and grease the CV ball inside the dc joint. Figured it was going to be at least $30 for a joint to do it myself anyway, so why not. Got it installed last night and will take a little test run this afternoon. Hope that solved all my problems. Really don't want to get into gear issues!