Yes, I forgot to mention: The sound is directional as it will move between speakers and fade away. However, I somehow cannot figure out what is making it. The sound, however, definitely does not belong in the game.
> Are you running any "environments"?
Yes, I'm running the "Living Room" environmental.
> You may want to close down some of the Liveware apps that may be running.
There're none running.
> increase the number of simultaneous waves that can be played
It is currently on 4. I'll increase when I play the Valley of Trouble scenario for a third time (I lost the previous two tries).