Every Character in The Walking Dead is Deaf
The walkers constantly sneak up on the characters. The walkers are not ninjas, so basically, the characters have to be deaf or going deaf not to hear those shambling lumps of guts and skin.
Just look at the pilot: Rick Grimes shoots a gun from inside a tank to kill a walker. That shot was so loud it made him deaf for awhile. All the close range gunshots going on all the time ruined the hearing of the characters, which is why then kept on attracting even more walkers.