It's sound effect #2 on the YouTube video above.
Anyway ... so I opened the door and kicked them out. And now they're hanging out in my driveway — making horror story dead kid/cat sounds. And there's no friggin' way I'm getting any sleep tonight. (update) So now I'm torn between "steering into the skid" and watching The Grudge - one of the few movies which actually creeps me out - or trying to figure out a way to get that eerie sound out of my head.