96 trooper front differential question

I have developed a clunk in the front differential. Seems to be from slack
in the front shaft. Real question: is the front drive shaft supposed to
rotate when a front tire is rotated (in 2wd). I thought the front wheels
should be free wheeling when in 2wd (from the shaft and front
differential). Maybe the front shaft has always turned with the wheels in
2wd (shaft free wheeling at the transfer) and I just never noticed. Are
the front wheels ONLY disenguaged by the transfer case? Just seemed
unusual to see the front drive shaft turning when I had a wheel off the
ground and rotated it???