2014 Tahoe No rear sound for dvd
 

My mother just purchased a 2014 Tahoe LT. it has a drop down DVD player on the ceiling. When we play a dvd the audio only plays on the front door speakers not in the rear speakers. I tried going into the audio settings and tried adjusting the ‘fade’ to ‘rear’ but nothing changes and the digital dial does not move! I tried moving the sound left and right and that works perfectly fine, also the digital dial moves. The radio audio plays through all speakers just fine. I don’t understand why the dvd sound won’t go to the back. I have a 3 year old and a 6 month old so this feature is very important to us. Any advice is welcomed. Thanks!