It's funny you say that. It actually only plays once an hour, no matter if there's an alert or not. If there's no alert you just hear that "This station is part of the Amber Alert Network" ID.
But for the last three days with the longer alert I've felt like it comes around a lot more often too.
Thats OK, cuz a recent alert was airing a full day and a half after the girl had been found and a half day after they had gotten the guy too! Good system, but it needs some work!