Sound of aliens? Eerie 'X-Files' noises recorded from edge of space

Mysterious 'X-Files' sounds have been heard 22 miles above the Earth.

The recording equipment, which was sent up by a graduate student as part of a Nasa project to record sound from the edges of the atmosphere, captured hisses and whistles in 2014, the Independent reported.

The microphones picked up infrasound, frequencies so low that they can't be heard by human ears, but speeding up the recordings means that the sounds can be heard.

The recordings were taken from a helium balloon in August last year. The and were one of 10 sent out by Nasa as part of the High Altitude Student Platform.

Daniel Bowman, the University of North Carolina student who captured the sounds, said that microphones dangling over New Mexico and Arizona helped get the first infrasound recordings ever taken at such altitudes.

Current guesses include sound from a wind farm, the ocean, wind or vibrations from cables on the balloon, according to Live Science.

The scientists will be sending more devices up as part of the 2015 run of the project, and hope that they can learn more then.

Bowman, who described the sounds as "like the X-Files," said that he was surprised by the sheer complexity of the signal, adding that he expected to see a few little stripes.