I'm surprised no one has posted about the show "Storm Chasers" and all of the siren audio it has. Mostly I've been hearing a Federal 2001 in the attack mode, but I'm pretty sure it's been stock footage, because they'll be driving along and one of the chasers will say, "Is that a torndo siren?" or, "There goes the tornado sirens," and they'll be driving down the road a distance and the siren remains loud, not like it fades off as they drive away.
Anyway, some very cool footage of tornadoes! I love that show. Last night's new episode was pretty awesome.