Did he use to work construction? Those jobs have all kinds of heavy machinery and tools that can cause hearing loss through time.
I remember one time when I was visiting family, someone was cutting metal wall frames (when they were already supporting a wall) with a reciprocating saw. It was so noisy. Almost borderline painful and they did it for a good bit of the day. And when it was over I swear I could still hear it reverberating in my head. I wanted to kick whoever it was in the butt.