Astronauts could only describe it as outer space-type music.
The strange, swirling sounds were recorded during the Apollo 10 mission, which orbited the moon two months before astronauts landed on it in 1969.
During the orbit, the spacecraft was out of radio contact with mission control for about an hour as it passed the far side of the moon. However, a recorder on the Apollo module captured the events on board during that time.
The recordings were classified and kept in NASA archives until 2008.
They are the subject of an upcoming series NASA's Unexplained Files.
The crew, which included astronauts Thomas Stafford, John Young and Eugene Cernan, were recorded discussing the sounds.
"It sounds like, you know, outer space type-music."
"You hear that? That whistling sound? Whooooo."
"Well, that sure is weird music."
The crew even debates telling mission control about the incident.
"It's unbelievable. You know?"
"Shall we tell them about it?"
"I don't know. We ought to think about it."
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