Photos: Apollo 11's Forgotten Astronaut
The May 1969 tapes were recorded while Stafford, Young and Cernan were on the far side of the moon, out of radio communication with Earth. The whistling sound lasted nearly the entire hour the astronauts were out of touch. Later, the recordings were sent back to Mission Control where they were transcribed, archived and classified, per protocol.
The conversation was eventually unearthed in 2008.
Some technicians have speculated the sound may have originated from interference from VHF radios on the command module and lunar module interacting with each other, according to researcher and author Andrew Chaikin.
Lunar Phases: The Changing Face of the Moon
But not everyone buys that explanation.
"The Apollo 10 crew is very used to the kind of noise that they should be hearing," Apollo 15 Command Module Pilot Al Worden said in a clip from the episode. "Logic tells me that if there was something recorded on there, then there was something there."
This originally appeared on FoxNews.com/SciTech