I've experianced this a total of two times now. When I bought Counterstrike: Source a few months ago, it did this and would never stop. Now, I just downloaded a game called World In Conflict, and it's ALSO doing it and I have no idea why.

What's happening is the sound is all grumbly and the music is de-tuned and what-not. The sound for everything(when i clicked buttons, voices, music, weapon soundfx) was completely messed up and it's not my card, speakers, or any of my hardware.

Anyone know what the problem is???
Try re-installing it. If that doesn't work, it's most likely some form of lag.
Play the man, Master Ridley; we shall this day light such a candle, by God's grace, in England, as I trust shall never be put out.