Residents of downtown Salt Lake City have reported hearing strange music coming from the sewers, sparking some to speculate that the sound may have extraterrestrial origins.

“[It was] just really kind of eerie, but it was beautiful,” Rosemary Olsen, a musician and downtown resident who reported hearing an augmented B chord repeatedly outside her window, told news station KSTLV.

Olsen told the outlet that she posted about the noise on the neighborhood app Nextdoor, where other residents reported hearing similar tones.