What the hell kind of bird is it that makes that amazingly loud rattlesnake sound outside every morning and evening?
Tell me its on the endangered list!
My guess would be a kingfisher. I have one that lives near my office on a creek, and he sounds kind of rattle-snakey.
This site has an mp3 of the sound he makes, in the menu on the left.
It would help if you’d say where the bird has been heard, and the nearby habitat. The kingfisher certainly seems like a good candidate, but only if there’s water nearby.