The Service Dept. couldn't duplicate the problem. The 4HI noise has magically disappeared, leaving me to believe that the clanking sound was caused by a 13mm socket I lost while installing my lift in November. We looked all around and under the KJ that day but never found that socket. I just assumed it would fall out along the road at some point. I guess it found a home somewhere in the front drivetrain and became dislodged on the way to the dealership. The dealership offered no possible cause but said that I should bring it back ASAP if I hear the clanking sound again and they'll waive the diagnostic fee. I was charged a half-hour of labor ($42.50). I used 4HI on a snow-covered cul-de-sac by my workplace, and as far as I could tell, the front wheels were getting power. At lunchtime today, I'll visit a nearby gravel road and test some more. Dealership said my 4WD was working normally, but I've learned to take a dealer's words with a grain of salt.
On the bright side, I finally got my new rear wiper blade.
T.J.