Vibrations that can be isolated to the transfer case are never good. With that said why can it not be fixed? I have to agree with TsiArt that on any vehicle that new and the cause can be isolated to the transfer then case make them replace the case. If it is because they are to lazy to look for it ( the problem) then that is another problem. Vibrations can come from many things drive shafts, wheel bearings, shocks, diffs, wheel alighnment, flat spots in tyres, brakes not ajusted properly easy to see why they might be not interested in looking for the problem.
Give us some more info and everyone here might be able to help. What makes them think that it is the transfer case?