This probably isn't a Mustang related question but more of a general car thing... but when its really cold out (as in 10 degrees or lower) and my mustang has been out over night (no garage for me) it makes this high pitched whistleing sound when I turn it on. It lasts for a minute or so until the engine warms up a bit. I've got a 2000 V6... any ideas what it might be?