Weird:

'Residents from Chula Vista to Oceanside reported a large rumble around 12:45 p.m. Friday.The mysterious sensation was described by some people as sounding like a door slamming while others said it was strong enough to rattle windows.A check of the U.S. Geological Survey website showed no earthquake activity.NBC 7 San Diego's Dagmar Midcap was in Del Mar at the time and described it as a "Sonic 'rumble'" She tweeted, "according to my contacts at USGS, not seismic but rather sonic."'

Creepy:

'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.'