I'm in an mine and I heard a gong sound. I am hiding. I heard footsteps, but I'm afraid to see what it is.
I was just listening to music disk "c418-13" and it sounds kind of like the gong sound i heard earlier.
It just means you are close to an extremely large, dark area. Usually happens around the super tall crevices. Occasionally around dark room spawners. Or...the staff is following you! Just kidding.