What does he hear

There was this man in a mental hospital. All day he would put his ear to the wall and listen.

The doctor would watch this guy do this day after day. So the doctor finally decided to see what the guy was listening to,so he put his ear up to the wall and listened.

He heard nothing. So he turned to the mental patient and said, “I don’t hear anything.”The mental patient said, “Yeah, I know. It’s been like that for months!”