Consider it one of the "Sounds of Freedom".
Could have been an Alert which often occurs on military bases. When I was on active duty I remember they mixed things up in order to keep us on our toes. Sometimes just an alarm in the barracks and at others sirens, alarms, PA's, and Ammo trailers delivered to the Company area.
If you didn't see it on Kiro TV or read about it in the Newspaper, it was most likely a training activity.