Sorry, Pink Floyd, you no longer hold the sole claim to sounds from the dark side. In an upcoming episode of the Science Channel's NASA's Unexplained Files, audio from Apollo 10—which flew to the far side of the moon in 1969, two months before Apollo 11's moon landing—reveals conversations among the astronauts as they hear odd sounds from the cosmos through their instruments, CNN reports. "Did you hear that whistling sound, too?" one asks. "Sounds like … you know, outer-space type music," another answers. "I wonder what it is." Whatever "it" was, astronauts Eugene Cernan, John Young, and Tom Stafford were wary of informing their higher-ups what they were hearing while out of contact with Earth. "Shall we tell [NASA] about it?" one asks, per Fox News. "I don't know," says another. "We ought to think about it." They opted for silence, thinking such a report might "cast doubt on their suitability for future spaceflight," per CNN.
The tapes were labeled "classified" after the craft returned to Earth and placed in the space agency's archives, the New York Daily News reports. The transcripts were revealed in 2008, but this is the first time the audio has been publicly heard. In addition to "we're not alone" speculation, one theory for the eerie sounds, which lasted about an hour, is that charged particles may have clashed with a magnetic field, RT.com notes (though it adds the moon doesn't have a magnetic field to speak of). Meanwhile, per CNN, a NASA technician who's interviewed on the Science Channel show insists that "radios in the two spacecraft [the lunar module and the command module] were interfering with each other"—an assertion that ex-astronaut and show voice-over Al Worden disputes. "The Apollo 10 crew is very used to the kind of noise that they should be hearing," he says during the broadcast. "Logic tells me that if there was something recorded on there, then there's something there." (NASA erased original footage of the moon landing.)