Mystery boom (stock)
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Numerous people reported on social media that they heard a loud ground-shaking boom around 9 p.m. Monday night in Clemmons and western Forsyth County.

However, state and federal officials say they don't know why it happened or what it was.

Scott Sharp, a meteorologist with the National Weather Service in Raleigh, said the boom could have been distant thunder coming from storms that moved through Davie, Yadkin, Stokes and Davidson counties at the time.

Dan Blakeman, a geophysicist with the National Earthquake Information Center in Denver, said there were no reports of earthquakes anywhere Monday night in North Carolina.