This is the sound I normally hear in short bursts.
This sounded on Sept 1, 2010 at about 19: 20, just once.
Sometimes it is repeated, usually three times.
Since I have been filming, this sound is sounded for shorter intervals.
Yesterday, it went off every time I tried to tape it.
On August 17th, this blasted in my room for about a minute at at time, three times. It sounded like a space ship from a B Sci Fi flick from the '60s. I felt very sick, so sick; it didn't occur to me to tape it until it was almost over. I only got the last second of it, which I uploaded on Facebook.
LRAD, Long Range Accoustic Device, Weapon