This is probably going to be an unpopular opinion, but here it is anyway. If it doesn’t come off with dish detergent and a scrub sponge, just call it a permanent seasoning and let it be. If scrubbing it like mad won’t make it come off, then it won’t come off if your food touches it.

Maybe you’re picking up on how sound is bouncing off the object, kind of like a really weak form of echolocation, and your brain doesn’t know how else to present that information other than to give you a visual.