Mississippi Emergency Management Agency spokesman Greg Flynn said he heard two booms about 8 a.m. as he walked into the office.

"It was loud enough that it made me turn my head," Flynn said. "I thought it was coming from the (Mississippi) Fire Academy, but there was nothing going on there."

A caller in Jackson said he heard the boom, which he thought was coming from Pearl, as far away as downtown Jackson.

Another caller said the lights went out briefly between Pearl and Brandon after he heard the boom.

Entergy spokeswoman Mara Hartmann said there was a 3-4 minute transmission-related outage Thursday morning near Old Fannin Road in Flowood that affected industrial customers, but no residential customers. She said that the cause is under investigation.

"It could be linked to that, but we don't know. Transmission (technicians) will have to walk the lines to find out where it came from," Hartmann said. "It might have been us. We just don't know."

A spokeswoman with the 172 Air Wing said they didn't have any planes flying Thursday morning, but a witness may have gotten to the bottom of the mystery. The sound could be coming from a tree cutter truck that's working at a building site behind Academy Sports in Flowood.

"The machine, every time it hits the tree, it goes, 'boom,'" a spokeswoman said. "It's a truck that's making the sound when it hits the tree, and it makes another boom when the tree falls."

A Belhaven resident posted on Facebook that the sound could have come from a storage container that was dropped at a construction site at the University of Mississippi Medical Center.

The official source of the sound remains a mystery.