What kind of nocturnal animal in Michigan makes a sound like a rattlesnake and cat hiss in trees at night?

We live in a southern Genesee county subdivision, and every night we hear this new sound coming from many of the mature trees on our block. It is not cicaidas, because there is really no pitch or tone to the sound, it literally sounds like if you mixed a rattlesnakes rattle with a cat's angry hiss, and it's pretty loud. Also, the bats that live around here are all small, and don't produce this kind of volume, unless its groups of them or something... I haven't turned up very much on the internet, and we're trying to figure out what these things are because it's creeping us out!!!