Galveston - Some island residents, firefighters, police and city hall officials heard a loud boom Wednesday, but the source of the noise remains a mystery.

Galveston Fire Chief Jeff Smith heard the explosion shortly before noon as he traveled on 12th Street.

City spokeswoman Alicia Cahill was at city hall, and police spokesman Lt. Jeff Heyse was at the police station when they heard the noise.

"We had several calls come into dispatch, and we sent an engine company out to investigate," Smith said.

One person called from 42nd Street, and the noise was heard as far west as 61st Street, Smith said.

"I was actually coming up on 12th street, and it was clearly a very loud noise," Smith said.

Firefighters found no fire and documented no sign of an explosion.

"At this point, it's possibly going to be an aviation aircraft or possibly a large transformer bank," Smith said.

The noise wasn't related to any transformer failure, and CenterPoint Energy had no reports of electrical problems, Keith Gray, a spokesman for CenterPoint Energy, said.

No one reported hearing the noise in Texas City, just north across the bay from Galveston. The noise wasn't related to any of the Texas City plants or refineries, Bruce Clawson, the city's Homeland Security director, said.

The noise could have come from an aircraft breaking the sound barrier. The tower at Scholes International Airport in Galveston, however, had no jets in the area at the time of the boom, airport Director Hud Hopkins said.

F-16 pilots that fly from Ellington would normally make contact with flight controllers at the tower if they were in the area, Hopkins said.

There were no reports of aircraft leaving Ellington Field or William P. Hobby Airport in Houston that would have created a sonic boom, Marlene McClinton, a spokeswoman with the Houston Airport System, said.

The Federal Aviation Administration also took no reports of a sonic boom, Lynn Lunsford, a spokesman for the administration, said.

Attempts to reach a NASA spokeswoman for comment were unsuccessful.