So what did the government do, planes/jets? Says sound cannon, what is that? And furthermore, WTF! A peacefull protest, what were they trying to achieve? How sad do you have to be to order this action, let alone to actually do this as an employee??
LRAD. Wouldn't surprise me if they were field testing the gear for the yanks or whoever. Would also explain why they did it in the middle of a "moment of silence".