The first time I drove up on one of the Ancient Relics and it popped out of the ground to my right, just off screen I was sure I was about to be blasted. Did not catch it on video though sadly. The one I ran across was at
Also I did not get much out of a spectrogram just muddy mush but the sound is like that, very low and droning minus that odd melody in the background that repeats. It is probably worth further investigation, like just about everything else. The Devs seem to have some kind of a reason for all of these little clues and hints even if they are not fully understood at the time.