Tucsonans flooded social media sites Wednesday night speculating on what caused a loud boom heard — and felt — over a chunk of the city.

Tweet messages started about 7:45 p.m., many from residents of Tucson's west side, saying a large explosion rattled windows at some homes.

Tucson police received reports of two jets flying over about 7:40 p.m., just seconds before the boom was heard, said spokesman Sgt. Chris Widmer. But it still isn't known it was a sonic boom.

The Pima County Sheriff's Department still doesn't know what caused the boom. But it has ruled out Davis-Monthan Air Force Base, Pinal Army National Guard, Tucson International Airport, the area's copper mines, Southwest Gas, El Paso Gas and Tucson Electric Power as sources, said sheriff's spokesman Tom Peine.

The area's Northwest Fire District received about 100 calls in a 15-minute period, said its spokesman, Capt. Adam Goldberg.

"We heard and felt out near Tucson Estates,” Kathy Nelson Ricker posted on the Star's Facebook page.

 One resident at River Road and Campbell Avenue says she even looked outside to see if a car had slammed a house.

  And people at a call center at River and La Cholla said it seemed to shake their building.

Senior Editor, News, Arizona Daily Star, Tucson, Az.