I got this from The Oatmeal (actually, after clicking something within the link KSUViolet posted). Supposedly, this sound is generally only heard by people under 25. Malls will play it to keep teens from lingering. What say you, GC? Can you hear it (and if so, are you under 25)? Even with my comp on the lowest volume setting, I can still hear it--and it's annoying enough to make me move. It's the same sound that TVs and other appliances make--I can hear those, too.
http://theoatmeal.com/quizzes/sound/