Plenty of people have oddball things going on with their senses that they aren't conscious of. I knew one guy who wasn't aware of his colorblindness until he ow

Plenty of people have oddball things going on with their senses that they aren't conscious of. I knew one guy who wasn't aware of his colorblindness until he owned some navy and some black socks that were otherwise identical, which occasionally had humorous results, and another guy who couldn't get into the AF academy because of a similar problem (much less funny). Being unaware of a problem with hearing is similarly easy. If a problem doesn't cause physical pain, doesn't have any real-world consequences, and doesn't physically manifest full-strength all at once, the brain can do a lot to keep us from noticing the existence or the progression of the problem.