I guess I wasn't very clear in my first post and maybe sounded sarcastic (shocker, right?) But if you buckle the unused seatbelts it should cut down on the flapping
I mean on the pillar where the belt runs parallel to itself, the belt slapping itself is what makes the annoying sounds. People also make things like this (below) for the Jeep, it's only a matter of time before they make the same exact thing and slap a Bronco label on it...
I know a lot of Jeep guys that just buckle the seat belts. Another thing you can do is get velcro straps to hold the top of the belt together but if you have passengers they'll have to undo them.
Don't be afraid to ask. I'm excited that the Bronco is opening up off-roading to people who never cared for it before.
To make it super simple for you:
If conditions gave you no troubles in a 2wd vehicle, leave it in 2wd.
If conditions gave you trouble/made it impassable in a 2wd vehicle...