Crickets are known for their chirp (which only male crickets can do; male wings have ridges or "teeth" that act like a "comb and file" instrument). http://en.wikipedia.org/wiki/Cricket_(insect)
The humming of all the damned fans in my computer case. Damn, I need to buy a system that doesn't sound like a cross between a Chinook helicopter and an X-wing fighter! (Star Wars stuff)