If you've noticed a really loud, annoying sound in the middle of the afternoon on campus, it's this guy:
Cicada. Photo thanks to S.
It's a cicada, and he's calling out for a mate. Apparently the sound production is related to hot weather, so they can be heard during noon but I have also heard the cicadas calling late in the evening in the campus. The sound is ear-splitting, especially if you go closer. When there are two or three calling at once, it can be quite painful.
There's a very nice section devoted to cicadas on one of the Planet Earth series and it shows a species of periodic cicadas, whose nymphs emerge after 17 years from the ground. Not all species remain underground for so long though, some are annual and others stay for 2-5 years (wiki).