I can't get the factory wireless headphones to play any sound from the DVD player. There's power (power light on, can hear a beep when pressing channel button), so the batteries are fine. Any suggestions?

 

It's a 2015 btw. Not sure if it matters, but did want to mention it...Also, everything else works fine. DVD plays with audio through speakers in normal mode, and plays in rear video monitor without sound through speakers when "radio" is pressed (the radio plays through speakers). Of course, this is when I'd want the wireless headphones to work (I can listen to radio while driving, kiddos can watch/listen to movie in back)...