For hundreds of years, people in the United States have occasionally been hearing mysterious, eerie rumbling and roaring sounds of an unknown origin. It seems that in many cases the noises are not related to earthquakes, but rather something happening in the atmosphere.

Where do the mysterious sounds come from? Image credit: Peter Hammer

In fact, the strange sounds, which are also described as ‘rushing’ and ‘rolling’, are not only heard in America: from Slovakia to India, they have been reported in many parts of the world. During the coronavirus lockdowns, in particular, many similar cases have been documented, probably because noise pollution was less due to the restrictions, so environmental sounds could be heard better.

Two particularly interesting occurrences were a Darth Vader breathing-like noise in Bratislava and a boom noise heard by residents of Texas.

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Although many of the booms that people hear or experience are obviously related to human activity – these could include explosions, nearby construction, a large vehicle going by, or sometimes a sonic boom -, the reports often cannot be explained by man-made sources. Some of these unaccountable occurrences are associated with various natural phenomena, like earthquakes, but the source of others remains a mystery.

There are places around the world where these mysterious sounds occur regularly. In the Ganges delta and the Bay of Bengal they are known as ‘Bansal guns’, in Shikoku, Japan, as “yan”, and in Belgium “mistpouffers” (fog belches). And loud banging noises are particularly often heard near Lake Seneca in the Finger Lakes region of New York. Known as the ‘Seneca Guns’, the sounds are so loud they sometimes can rattle windows and doors.

Coastal North Carolina residents also often report hearing similar unaccountable booming noises, with explanations ranging from distant storms or earthquakes, to quarry blasts or even military exercises. Now, a group of experts decided to find out the truth, Live Science reports.

The team at the University of North Carolina at Chapel Hill used seismic data recorded by the EarthScope Transportable Array (ESTA) since 2013, and compared it to news reports from North Carolina, where the noises were reported fairly often. They didn’t find any events that were consistent with earthquakes.

“Generally speaking, we believe this is an atmospheric phenomenon – we don’t think it’s coming from seismic activity,” researcher Eli Bird told Live Science. “We’re assuming it’s propagating through the atmosphere rather than the ground.”

At this point, the researchers decided to focus on listening to infrasound data – low-freequency sound which cannot be detected by the human ear. They did pick up signals varying between 1 and 10 seconds in length, that were associated with the reported boom events.

According to the team, although these signals may indeed be related to the observed sound phenomena, they do not bring us any closer to solving the mystery of the noises, nor whether they are caused by the same type of event. Many could be sonic booms from aircraft, storm waves and even tsunamis being amplified in a particular direction, or the sound of igniting methane gas released from methane hydrate beds. And there is another, even more interesting option: bolides – meteoroids that go unseen but still produce a sonic boom in the upper atmosphere.

For now, however, more data needs to be gathered to find the real source of the noises.