This is a recording a friend of mine did for me back in 2002, just after Emergency Management installed a single tone Modulator on the Belknap campass at the University of Louisville. After the Mod turns off, you can hear some Thunderbolts for a while. One of them has a rotator that is set to 8 RPM. This is not a very loud Modulator, because you can't hear it that well on the other side of campass. I believe it's one of the 110 DB models. The dual tone Modulator at Water Front Park is much louder, though I don't have a recording of it yet. Hope you enjoy this one.
http://media.putfile.com/Single-Tone-Modulator-in-Alert
Edit: Here's a direct link to the file.
http://www.fileden.com/files/2008/2/3/1 ... 0Alert.mp3?