Dogs when they howl at sirens...

If u pay close attension, your dog also howls when certain music is played. This is call pitch in tune. All noise..Ha Ha

some dogs do, some dogs just don't. and it's because its a high pitch sound and it sometimes make them react that way.

I guess it's a dog's natural reaction to such a weird sound. I notice that dogs are very sensitive to sounds. When there's too much noise they will even get scared and try to hide. The first time they probably heard the siren, they must have hidden themselves like crazy, and now that it has become like routine for them to hear it, they probably feel something is wrong that is why they howl.