Yesterday, thousands of residents across New Jersey, New York, Maryland and Connecticut reported bizarre rumbling sensations, despite no earthquake activity being reported. Cue the "X-Files" theme tune.

At 1:24 p.m. EST in the afternoon of January 28, the first tremors were recorded northeast of Hammonton, New Jersey. In the next hour and a half, nine more were recorded as far up the east coast as Long Island, New York, according to the U.S. Geological Survey (USGS).

The event was initially thought to be an earthquake, prompting thousands of tweets and 911 calls to report they were feeling earthquake tremors.

Unconfirmed reports of an earthquake in NYC/NJ area. No earthquake activity identified by US Geological Survey. No reports of damage.

— NYCEM - Notify NYC (@NotifyNYC) January 28, 2016

However, after no earthquake activity or destruction was reported, scientists started to think the vibrations picked up on their seismometers could have actually been from a sonic boom. These occur when an object or explosion travels faster than the speed of sound; that’s over 1,225 kilometers per hour (761.2 miles per hour) at sea-level air.

Then came the issue of figuring out what caused the sonic boom. Gizmodo reports that even the USGS didn’t know what had caused it at first, responding to an inquiry with the statement: “We don’t know what for sure.”

It’s illegal for civilian aircraft to break the “sound barrier” in the United States under regulations from the Federal Aviation Administration (FAA), so heads turned towards the military. Yet, ABC News reported that three of the major military air bases and organizations on the east coast, McGuire Air Force Base, U.S. Federal Aviation Administration, and North American Aerospace Defense Command, all denied testing any supersonic aircraft that day.

After a few hours of confused panic, the U.S. Navy confirmed it was them all along. NBC News reported that the Navy had confirmed they were carrying out tests on a supersonic F-35C fighter jet over the Atlantic Ocean on Thursday afternoon.

The Navy has confirmed testing of supersonic aircraft offshore from where sonic booms and shaking were reported.

— USGS (@USGS) January 28, 2016