Aloy exhales in relief. Good. At least she's not losing it. Although it brings up a fun new mystery: where, in fact, is the music coming from?

She hums in agreement—it's definitely not live. A recording, then?—and wades through the doorway to get a closer look. The room is half-flooded, so anything they can hear... "Has to be above the water line."

Further in the chamber, there's a dais raised above the water, but Aloy ignores it after a cursory glance. It's not what's making the noise.