The engaging/disengaging mechanism is a sliding, splined collar... both in the front axle ADD unit and inside the (at least the part time 4x4 drive) transfer case so any noise it makes is much like engaging/disengaging gears with no synchronizers... Not sure about the full time transfer case...

So it is totally dependent upon you to make sure there is no relative speed differences between the front and rear axles and therefore the recommendation to be driving in a straight line and if binding turning the steering wheel slightly to the right and left to unload any binding... and of course always have the exact same size tires between the front and rear....