This one was recently posted to Youtube. It's not as loud as it should be, and it sounds terrible. That popping you hear is not from the recorder, but it's from the siren. Listen as the siren just fades out completely, then abruptly comes back on for the winddown. The person who made the video thinks the siren may have a bad driver.
http://youtube.com/watch?v=mMChz-0juM0
You can also hear a Whelen in the video.