User blog comment:IamJakuhoRaikoben/Chapter 518: Master Enchant, Review./@comment-7418318-20170121101147/@comment-5303512-20170123154246

If the room was on the surface that would make sense that it would make a noise, but It all determines if the room underground is deep and that makes it sound proof from the surface.

That rock is a powerful version of Sema, plus it is enchantment which does mean it does have magic.

Well Brandish powers has shown consistency so far, there would be no way it wouldn't now.

Besides, as a badass, Erza has to destroy it, its the only explanation.