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LOCHBUIE, Colo. — People in Lochbuie heard a loud boom around 9 p.m. Monday.

They were calling it the “Big Bang Theory” when talking about it Tuesday because they don’t know for sure what caused it.

Some people in Brighton reported hearing the very loud noise, too.

Police said there were no reports of injuries or property damage as a result of the tremendous boom, but some residents have a theory about it.

“I heard a dull roar,” U.S. Navy veteran Michael Grainer said. “I looked out the door and I heard it, boom, just like that, and it shook everything.”

So what does he think it was?

“Speed of sound being broken,” he said.

The Lochbuie Police Department said there is no investigation because there was no damage or injuries, but it is also curious what caused the loud sound.