In May 1969, the Apollo 10 astronauts heard strange noises as they circled around the dark side of the moon just months before astronauts made the first-ever steps onto it, according to NDTV. Now, NASA has made the recording of the strange "music," which was heard while out of radio contact with the Earth, available for the public to hear.

The sounds, which lasted for approximately one hour, were recorded and transmitted to mission control in Houston by the three astronauts on the Apollo 10 - Thomas Stafford, John Young and Eugene Cernan. Although a transcript of the text was made available back in 2008, this is the first time that the audio has been made public.

"You hear that? That whistling sound?" asks Cernan, describing the sound as "outer-space-type music."

The sounds were so strange that the trio were skeptical about even telling their chiefs at NASA for fear that they would be ridiculed and possibly lose their chance at future space missions.

NASA states that the sounds are not alien music, claiming that they likely came from radio interference from the lunar module and the command module that were in close proximity.

Strangely enough, Michael Collins, the pilot of Apollo 11 who flew around the dark side of the moon by himself while Neil Armstrong and Buzz Aldrin walked on the surface, also claims to have heard the eerie sound, although he believes that radio interference is an acceptable explanation. Furthermore, when the module landed on the surface, the noise stopped, CNN reports.

The dark side of the moon, although shielded from Earth radio transmission, is radio-noisy due to the ambient static that results from the storm of electromagnetic frequencies that make their way from deep space, suddenly becoming audible, according to TIME.

Take a listen to the "moon music" below.