It's not clear what caused those booms that rattled North Carolina's south coast last week. But methane escaping from the ocean or even a small meteorite have been suggested as culprits.
John Huntsman is an associate professor of geology at the University of North Carolina-Wilmington. He heard a boom on Friday but isn't sure of the cause. There was a second Saturday.
It wasn't an earthquake because there was no seismic activity. Military bases reported no aircraft exercises.
Similar booms have been heard along the South Carolina coast in the past. Suggestions have included methane bubbles being released below the ocean and breaking the surface.
Huntsman says some scientists have suggested they are caused by tiny meteorites hitting the atmosphere.