A big boom, followed by earthquake-like tremors. That's how people are describing what they felt Thursday morning.

Starting around 9. the Count on 2 newsroom started getting calls into our newsroom from viewers, from Johns Island, up to Isle of Palms and McClellanville and all the way over to Nesmith.

South Carolina typically sees 10-15 earthquakes a year. But, we don't feel most of them.

The National Earthquake Information Center says this isn't an earthquake since nothing was recorded on their seismographs. They say it was most likely a sonic boom. But the Charleston Air Traffic Tower says nothing was in the area that would have produced that sonic boom.

The majority of people Count on 2 spoke with say they did not feel a thing this morning. But, there are some who say they definitely felt a rumble.

"I literally felt my house shake, vibrate," explained Isle of Palms Resident Gloria Hewitt. "It was really loud, real loud and I heard my china shaking in my china cabinet."

"The ground was shaking, the house was shaking, the windows were banging," said Isle of Palms resident Daniel Davis.

Both Hewitt and Davis are asking one question: what was it?

"An act of God,' Hewitt thinks.

"Either the wind, an airplane or an earthquake," said Davis.

Davis would put his money on it being an earthquake. He's lived through three before. But still, this one shook him up a bit.

"You didn't expect for there to be an earthquake in Isle of Palms this morning," he said.

Even the National Weather Channel was reporting a possible earthquake felt in the Charleston area.

All those who felt it say it lasted seconds. While it may have come and gone as quickly as a gust of wind, the mystery of what it was is sticking around.

There is another possible explanation for this mystery. According to the US Geological Survey.

There is an unexplained phenomenon called Seneca Guns that sound like sonic booms and shake homes.

There have been reports of Seneca Guns along the coasts here in South Carolina and also in North Carolina and Virginia.

In addition, there have been reports of such booms around Lake Seneca and Lake Cayuga in New York State.Some speculate this could be gas escaping from vents in the earth's surface, but no exact cause is known.