From the ESA description:
"Rosetta’s Plasma Consortium (RPC) has uncovered a mysterious ‘song’ that Comet 67P/Churyumov-Gerasimenko is singing into space. The comet seems to be emitting a ‘song’ in the form of oscillations in the magnetic field in the comet’s environment. It is being sung at 40-50 millihertz, far below human hearing, which typically picks up sound between 20 Hz and 20 kHz. To make the music audible to the human ear, the frequencies have been increased in this recording. Original data credit: ESA/Rosetta/RPC/RPC-MAG. This sonification of the RPC-Mag data was compiled by German composer Manuel Senfft (www.tagirijus.de). Thumbnail image credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0"