For those of you saying it's something with the parking pawl, do this: Go put your transfer case in neutral. Start the jeep, put it in drive, then put it in park. You'll hear the noise he's talking about.
What you have here, JMO, is an issue inside the transfer case. On a wild guess, I'd say the shift forks weren't aligned properly and it's just staying in neutral. (Transfer case neutral, that is). You need to take the case back off and crack it open again. Diagnosis without the vehicle in front of you is difficult, but this is a no-brainer. The t-case must come back off, and you need to find out why it's staying in neutral.