A calliopean sound is sharp and high pitched, like the calliopean whistle of an angry lifeguard who's fed up with all the kids running around the pool.
The adjective calliopean comes from calliope, an old-fashioned musical instrument with a distinctively shrill, loud sound. Strangely, the word's source is Kalliope, the ancient Greek Muse known for her lovely voice. Calliopean sounds are quite the opposite: harsh, piercing noises that make you want to put your hands over your ears, like the screech of an owl or the unpleasant shrill of nails on a chalkboard.