Played through it on single player twice now and twice the same thing happened:
When you meet up with the marines to help out some other marines (Semper Fi or Die mission) they keep telling you to "move up, go" over and over again until you beat the part where you reach the "swarm Gun" near the bridge then it stops.
the 2nd sound issue i had was when Prophet is blabbing on near the end of the game it jitters the sound like mad.

I noticed this on my third play-through(first issue), I Lol'd =]