The escalating sound produced by a large group of tweens. At first, the sound is a light chatter. Then it grows in intensity and the frequency changes to a squeal. Eventually the incoherent ramblings of these little pricks drowns out all ambient background sound until you get a massive migraine.
After my buddies and I walked out of the movie theater we noticed a large group of tweens waiting around for mommy and daddy to come in their BMWs & Lexus to pick them up. Their tween spastics were so deafening that we started to bleed from our ears.