I suggest you read Edward Feser’s article which addresses ear plugs, which I would argue have similar functionality as ear muffs:
“First, it cannot be repeated too often—if only because some critics seem to want to attack nothing but straw men—that the perverted faculty argument does not entail that there is anything wrong with the use of man-made devices, or the use of a faculty for something merely other than its natural
function, or the interference with natural processes where plants, non-human animals, or inanimate objects and processes are concerned. Nor is there anything ad hoc about this, for the whole point of the argument is simply to draw out the implications of the Aristotelian-Thomistic position that what
is good for us can in principle only be what is consistent with the realization of our natural ends. And neither artificial devices, nor the pursuit of ends other than our natural ends, nor interference with non-human natural processes are inherently contrary to the realization of our natural ends.Hence examples like chewing gum (which is merely other than, rather than contrary to, the natural end of our digestive faculties) or the use of earplugs (which though artificial facilitate the realization of our natural ends insofar as they protect the ears from excessive noise, facilitate sleep, etc.) and the damming of rivers (which doesn’t even concern human faculties in the first place) simply miss the point of the argument.”
Full article here:
https://drive.google.com/file/d/0B4SjM0oabZazWC1SRmN0WXVpYkE/view