Mysterious booms heard south of Burlington Saturday night have many residents scratching their heads.

Law enforcement dispatchers said residents in Wever, West Point, Fort Madison and Keokuk reported hearing a loud noise -- strong enough to shake a house -- between 6:30 and 7 p.m. followed by other lesser booms at varying times Saturday night.

Law enforcement officials have theories about what caused the sounds but no concrete answers.

"I have no clue (of the cause)," said Lee County Sheriff Buck Jones. "I don't know of anyone blasting around here."

Jones said he wrote the incident off as explosions at the Iowa Ammunition Army Plant. But no munitions are tested after dark by American Ordnance, which operates and maintains the plant.

"It wasn't us on a Saturday night," said Doug Hanify, deputy director of business development for American Ordinance. "We don't test at night time."

Another theory was that the sound was a sonic boom caused by a plane breaking the sound barrier, which is what Lee County Emergency Management Coordinator Stephen Cirinna believes.

"It rattled my house in Montrose. ... At first I thought a tree had fallen on my house," said Cirinna, who grew up hearing the sound barrier being broken as the child of an Air Force veteran. "I'm passing it off as a sonic boom at this point."

However, Federal Aviation Administration spokeswoman Elizabeth Isham Cory said records Saturday showed no military or domestic aircraft in the area.

"We looked up the radar. We had no planes in the area. So I don't know what it was. It wasn't an aircraft," Isham Cory said.

But Cirinna said it still could have been caused by some kind of military test, which officials may not be forthcoming about.

A similar sound several years ago turned out to be a test of a military plane based at the Scott Air Force Base, east of St. Louis, Cirinna said.

This would not be the first time a loud noise in the area has gone unexplained.

"We had the same thing about a year-and-a-half ago during the warmer weather. Nobody ever figured out what it was," Jones said.

Alliant Energy spokesman Scott Smith suggested the source of the sound likely was electrical fuses blowing as ice and high winds of up to 45 mph caused power lines to cross.

"It's just like an M-80 going off," he said.

The fuses are designed to blow to prevent surges from traveling through power lines to substations and causing widespread power outages.

However, those who heard the sounds expressed doubts about the explanation.

Loud sounds also were heard in Kirksville, Mo., about 90 miles southwest of Keokuk, said David Hall, director of the Kirksville Regional Airport.

Hall said he heard the noise several times at home and compared it to a cannon being fired or someone pounding on a deck with a sledge hammer.

"I guarantee you I heard it," Hall said. "At first I thought it was popping and cracking from the cold. The temperature was just plummeting that evening. But it was obviously more than that.

"Several people heard it. Our (Kirksville) 911 dispatch center called and asked me if I knew anything about it. I don't have any idea what it was."