transfer case bearing, front output shaft

It could be many things, unfortunately and without hearing the noise first hand or being able to do some basic diagnostic tests its hard to say. It could be a wheel bearing or a differential bearing, gearbox bearing ect. A wheel bearing will make most noise when that wheel is "loaded" on a turn taken at speed say a bend on a country road 30mph. Jack up the car if it is a front wheel bearing that is bad you may feel excess play in the bearing if you grab the wheel top and bottom and 3 o"clock and 9 o"clock position.