Oh, THOSE!
Don't think there were any of those in Ann Arbor. Bloody thousands of them in DC though. I have never heard such a spooky noise before. At night it was incredibly eerie, especially around Scippy's area.
Funny story: we call at a shop so that Mav could buy some fags and us get some milk for morning tea. Get back in the car, just putting my seatbelt on, and there is this horrendously loud noise right beside my ear. One of the damn things had gotten in the car. Gave us a shock lol. it's noise is far greater than its size.