Why Does My Xbox 360's Game Audio Disappear?

Sometimes at around 9:00 when im playing call of duty the game audio turns off. i can hear all the players talking on their mics but the game audio disappears for no reason. this has only happened when im playing COD.

the xbox is really starting to make me mad and i dont want it turn into a sign of the rrod

also note that this is a used copy of the game but it works perfectly

Suggestion:

that sounds like a problem with your tv

try it on another tv, install the game to the hard drive