Clunking/4wd fault

So, my 2019 Explorer Limited Ecoboost has a clunking noise that my girlfriend says is coming from the rear. I've been trying to get it to do it and won't do it when I'm driving it.

She says on take off it will clunk and won't do it again. Then sometimes when put in reverse, it will clunk too. Today she was leaving work, put it in reverse and it clunked on her again. Then a message displaying "4WD fault service required" message come up on the screen.

So far. Everything is driving like normal with no issues to the drive train. I'm not hearing any roaring or whining noises indicating that the transfer case is the culprit. All 4 axles are intact, no play or obvious damage. Drive shaft seems intact with no play. Universal joints seem fine.

That leaves me stuck with the possibility of taking it to the dealership. I have wiggled and moved everything and nothing appears damageddor visually broken. Has anyone else had this happen to them? I am aware that Ford has had problems with the clips that the axles are held in by.