— -- The residents of Mount Holly, a town in North Carolina, have been puzzled by a mysterious "loud boom" that reportedly shook several homes earlier this week.
The Mount Holly Police Department "received more than 30 calls from various parts of the city and even neighboring communities" about the noise on Tuesday evening, said Chief of Police Don Roper.
"People were saying they heard a very loud boom or explosion or loud bang, and some folks said it shook their houses and rattled the windows," Roper told ABC News today.
"It sounded like a bomb just went off outside our house," one caller said, according to 911 audio obtained by ABC's affiliate WSOC in Charlotte, North Carolina.
Several officers immediately went out that night to check areas where callers reported hearing the sound, according to Roper.
But they found "nothing," he said. "There was no evidence of any type of injuries or damage."
There have been several other reports of similar loud noises in the area this past week, Roper said.
One was identified as a train releasing its air brakes and another was an "atmospheric disturbance" -- but what caused the "loud boom" on Tuesday evening remains a mystery, Roper said.
"There's certainly been a lot of chatter and theories on social media, but we weren't able to confirm anything," he said. "We do want people to know we do not feel there is any danger or cause for concern."