High-pitched sound plays unless a 3D application is used

[Calinou]

When I'm on the desktop (this happens with any DE/WM, LiveCD), an high-pitched sound always plays unless a 3D application such as a game is running. This doesn't happen on Windows (only when I'm playing games when I have more than ~200 frames per second being rendered, I can limit max FPS by using vsync to prevent that).

[HermanAB]

Probabaly feedback from one of your microphones to a speaker. Run the pulse audio volume control and turn down the mic.