I've had this little problem happen in 2 multiplayer/online games, a 2vs2 and a 4vs4:
The game plays fine then I jump to another star system and all the sound FX from the game die! The music still works, but everything else (the warning voices, battle sounds, etc.) is gone. It happened to almost every player in these games and I am hoping that it doesn't become a regular problem.
Has this been happening to anyone else?