R. Stickney, Lauren Steussy and Monica Garske
NBC San Diego 
June 30, 2012
Residents from Chula Vista to Oceanside reported a large rumble around 12:45 p.m. Friday.
Two months ago, when San Diegans heard a similar sound, there was evidence of chaff on weather radar . Chaff is a material sometimes emitted during military exercises.
On Friday, however, Tina Stall with the National Weather Service said there was no visible chaff in the area at the time the noise was reported.
“There was indeed an atmospheric tremor, or ‘skyquake,'” Walker said. “The likely cause of these ‘skyquakes’ is routine military activity very far off the coast of San Diego (at least 50 miles away) in zones that are designated military training zones.”
Typically, we don’t hear these “skyquakes.” But when the wind reaches speeds of over 100 miles per hour, the sound can reach parts of San Diego, Walker said.
A spokesperson from Camp Pendleton said Marines are not training with anything unusual. They often train with various military equipment and will be training with tanks both Saturday and Sunday.