Astronauts aboard the Apollo 10 spacecraft talked about a strange sound they heard when passing by the moon's dark side, a region inaccessible to communication from Earth.

According to transcripts of those conversations, which NASA released in 2008, the astronauts called the sound "music" that sounded like an "outer-spacey... whistling sound." The transcripts detail conversations between Thomas Stafford, John Young, and Eugene Cernan during their 1969 flight.

According to The New York Post, the Apollo 10 transcripts will be part of a series airing on the Science Channel titled "NASA's Unexplained Files." In a preview for the series, Apollo 15 astronaut Al Worden talked about what he would have felt if he heard such a noise when he made the flight in 1971.

"If I were to hear something back there... it would freak me out," he said. "The Apollo 10 crew was very used to the kind of noise that they should be hearing. Logic tells me that if there was something recorded on there, then there was something there."

But of course, the noise can be explained, contrary to the series' title. According to CNN, Worden says on the show the noise is not coming from the moon at all, but is actually the "radios in the two spacecraft [the lunar module and the command module] were interfering with each other."