It sounds as if he believes he is being gangstalked. This is almost certainly a mental health issue. His house mates don't hear or see these things because they are not actually happening. The person who thinks they are being stalked sees dark intent in everything and everyone. It generally reaches the point where he believes his friends and family are part of it. They often feed their fears by connecting with others who share their stories.
The best thing you can do for your friend is get him to see a doctor.