My brother's computer is making some random beeping sounds lately (it's like the motherboard's speaker's sound). It only occurs while he's playing games though. And it doesn't even happen with all games, but just some, which seems awfully strange to me.
It usually starts like a minute or so after he starts playing and it doesn't stop till he returns to the desktop (the funny thing is that even a alt-tab switch to the desktop stops the beeping, but it starts again if he returns in-game). I didn't notice any particular pattern in the beeping, it just seems random.