Most camcorder microphones aren't up to doing a good job recording loud sounds like a siren. Someone has to figure out someday the best combination of microphone and recording media to capture siren sound. A good rock-concert type mike might do the trick.
One reason why I think the T-bolt featured in the video sounds a bit muffled is probably the AGC (automatic gain control) circuit in the camcorder. It was just reducing the audio gain (to prevent overload / distortion), thereby taking out a lot of the T-bolt's punch while doing so. And most microphones built into camcorders, especially cheap ones, don't take hi-fidelity into account anyway.
ya pretty sure...look at the siren when they pass by it on the street, the blower is on the side of the pole. Plus you can the head rotating on it, and only one sirens makes that disctint of a wind down.