Back in 2009, the Cassini spacecraft picked up Saturn Kilometric Radiation, or SKRs, natural radio signals being emitted by Saturn. What was bizarre was the pattern of the sounds, which they couldn't explain -- it's actually two signals, one from the planet's north pole and the other from the south pole, in an out-of-sync duet [source: Space.com].
While these sounds normally would be inaudible to human ears, scientists have altered them to create really spooky-sounding recordings. (They sound a bit like bursts from an air raid siren.) As University of Iowa scientist Don Gurnett, who headed Cassini's instrument team, told Space.com, "These data just go to show how weird Saturn is."