Play a sound, any sound

bash (13)

sudo rm -rf /

The faster the hard drive the better the sound. Don't work with SSDs.
(Don't try this at home, sudo rm -rf / erases everything on your hard drive)

*sh (5)

eject

(does not work if you have no CD/DVD or similar drive..)

Befunge, 0

If I read the spec correctly, this is an endless loop.
Endless loop = you'll hear your CPU cooler spin up.