KGTV.com's newsroom began receiving reports of a possible earthquake from residents in the Mira Mesa and Clairemont areas at about 12:45 p.m. on Friday.
A check of the U.S. Geological Survey map of the Southern California region showed no earthquake activity, and USGS officials said earthquake activity was not responsible.
Since the initial reports, residents from as far north as Oceanside and south to Chula Vista have told KGTV.com they heard and felt a "rumble"-like sound.
An Escondido woman said, "I heard and felt the loud boom/2-to-3 second shake here in Escondido. Just as I was deciding whether to leave my desk, it was gone. It happened really fast but very noticeable. I wonder what it was!"
One Clairemont resident said, "We felt it in northwest Clairemont around 12:45. We thought it was an earthquake."
San Diego police Lt. Andra Brown said she felt downtown SDPD headquarters jolt a bit from inside her fifth-floor office. Likewise, Maurice Luque, spokesman for the city Fire-Rescue Department, detected structural jostling akin to a weak earthquake at his workplace.
Brown said two citizens, one in La Jolla and one in the Sunset Cliffs area, made emergency calls to report rattling windows and distant booms seemingly emanating from the west.
Sheriff's Lt. Paul Robbins said his agency had received "a couple of calls" from the public about the mysterious rumblings, but none that merited patrol call-outs.
Officials at Marine Corps Air Station Miramar said the sound did not come from the base.
Camp Pendleton officials told KGTV.com there was training on the base Friday, but nothing that would cause a sound similar to a sonic boom.
A Navy official said the sound did not come from any of their ships or aircraft.
No damage or injuries were reported.