2003 Tahoe  

My friend has a 2003 Tahoe with a built-in Panasonic DVD player and she can't figure out how to play the video with sound. The movie plays but the sound doesn't, not through headphones or through the vehicle speakers. In the owner's manual it says to press the SRCE button but whenever we tried that it would just switch from AM to FM. And in the manual it also says that a DVD symbol should appear on the front radio display but it didn't. So I was wondering how we should go about getting the audio to play with the DVD.