Hey waggin'ear, welcome to IFSJA. Good to see yet another NC jeeper.
About your questions....how fast are you going when the noise starts and are you in 4lo or hi? About your jeep staying 4wd, after you switch it back to 4hi, try going in reverse. That works on the QTs I'm not too sure about the NP 219, but its worth a try. Also you might not be completely in gear, that would account for the noise. Make sure that the lever is pulled all the way up, (pull it fast and hard), when in neutral at about 3-5 MPH.
Well, let me know more about this problem...
'77 Cherokee Chief W/T
QT w/low range
31" x 10.50" General Grabbers
My FSJ page