Sometime a few weeks ago I took my 360 over to a friends house. They have 2 huge HDTVs so we could play some awesome PD0 system link. I got there around 8pm and played some 4 man multiplayer for a while. About 30 mins later the second 360 turned up and we started playing 7 man system link (we were short one controller!). About 4 hours later my 360 sound went crazy. It was like one of the players had extreme echo on all their sound or something, along with a load of static. We tried exiting the session, still there. Quitting to the dash and restarting the game, still there. We had to shutdown and restart the xbox to get it fixed. Around 30 mins later the other 360 did the same thing.
I just thought it was weird that seemingly after a set time of around 4-5 hours the sound just goes nuts. We haven't had another session that long to know if this is a reproducable problem, but the fact that both boxes did it makes me think it could happen.