This is for you if you hear a buzzing sound from your headphones just at the moment when you start a 3D game.
This buzzing sound is caused by your VGA, modern graphic adapters emit a relatively strong noise when processing 3D images. Noting dangerous.
Many newer motherboards such as my Asrock X58 deluxe have the front panel connection just above the first PCI express 2 slot.
When you installed your computer, you must have let the front panel cable rest on top of your VGA (mine is a sapphire 4890 OC). At such a short distance electromagnetic coupling occur (electromagnetic waves are transformed into electrical signals creating a noise).
To reduce\remove this buzzing (humming) sound, make sure to move the front panel cable as far as possible fom the VGA .