In July 2015, scientists at the National Oceanic and Atmospheric Administration (NOAA) lowered a microphone more than 36,000 feet into the Mariana Trench. For the next three weeks, they captured a wide array of bizarre and unexpected signals, crafting an audio profile of the world's deepest point that one site described as "nightmare fuel."

As NOAA shared in a statement, even the deepest parts of the ocean are filled with a cacophony of sounds.

"The ambient sound field is dominated by the sound of earthquakes, both near and far, as well as distinct moans of baleen whales, and the clamor of a category 4 typhoon that just happened to pass overhead," they said.

One sound in particular, however, intrigued the scientists as it was unlike anything they had ever heard before. Lasting a little under 3.5 seconds, it spans frequencies as low as 38 hertz and reaches as high as 8,000 hertz in a "metallic ping" finale. You can listen to the bizarre clip below.

In a new study published in the Journal of the Acoustical Society of America, the researchers who recorded the sound believe it represents a new type of baleen whale call.

"It’s very distinct, with all these crazy parts," Sharon Nieukirk, senior faculty research assistant in marine bioacoustics at Oregon State, said in a statement. "The low-frequency moaning part is typical of baleen whales, and it’s that kind of twangy sound that makes it really unique. We don’t find many new baleen whale calls."

The unique call, now known as the "Western Pacific Biotwang" is similar in its otherworldly acoustic design to the so-called "Star Wars" call. That one, which you can hear below, is attributed to the minke whale, another deep ocean baleen species.

With a suspected source identified, the researchers' next move is to figure out the nature of the calls. Baleen calls are generally related to mating and only heard during the winter months, while the "Biotwang" call is year-long phenomenon.

“If it’s a mating call, why are we getting it year-round? That’s a mystery,” added Nieukirk. “We need to determine how often the call occurs in summer versus winter, and how widely this call is really distributed.”

A new expedition back to the Mariana Trench is currently being organized to capture acoustic and visual identification of the source and figure out how the sound is being used.

"It really is an amazing, weird sound, and good science will explain it,” Nieukirk said.

Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.

Bizarre Mariana Trench 'alien call' identified
Metallic noise, captured from the deepest point on Earth's surface, likely belongs to a species of baleen whale, scientists say.