A weird problem.. when a friend of mine goes to play a game of DoD I can hear all the sounds his game is making.. him shooting, jumping, anything like that. When I speak to him it transmits that back to me as well.. the funny part is he doesn't even have a mic

Any ideas what to do to get rid of this?
He has a Sound Blaster Audigy with the latest drivers and WinXP and TS2.0 ofcourse