An IMC reporter called in to tell me that the police, earlier in the protest, were using noise weapons to push people back. These things were mounted on the handlebars of police bicycles.

People shouted "turn them off, turn them off" until, finally, the police turned off the noisemakers.

At its peak, the march had around 1,000 people at the Westwood Federal building.

Here are some articles about sonic weapons:

http://www.defensetech.org/archives/001741.html

http://www.cnn.com/2004/TECH/ptech/03/03/sonic.weapon.ap/

http://en.wikipedia.org/wiki/Sonic_weaponry

http://www.npr.org/templates/story/story.php?storyId=4857417