The crew of an Apollo mission to the moon were so startled when they encountered strange music-like radio transmissions coming through their headsets, they didn’t know whether or not to report it to NASA, it’s been revealed.

It was 1969, two months before Apollo 11’s historic first manned landing on the moon, when Apollo 10 entered lunar orbit, which included traversing the far side of the moon when all spacecraft are out of radio contact with Earth for about an hour and nobody on Earth can see or hear them.

As far as the public knew, everything about the mission went smoothly.