3 Channel Audio

Hey there community!
This could possibly be a really stupid question but I'm asking nonetheless because I can't for the life of me figure out what's wrong. Here is the issue... I have 4 video clips that all run perfectly well but have no working audio. Except for one. After a quick comparison the only difference I found was that the working one had 16 bit stereo audio and the others only 16 bit... that's about as far as I've gotten... Any help would be greatly appreciated!  :)