On the subject of desensitizing. Joey used to run to hide anytime the front was opened and had not reaction if the door from the house to the garage was used. So I started to use the front door more and now she does not run away if one of us uses it. So it is possibly to get them used to somethings like the doorbell ringing.

However, if it is not just that the bell is a strange sound but that it bothers his ears or something like that. Then all you are going to do is drive him nuts. If you can put in a new bell and see if he reacts the same. If he does I would say it is just that the bell is a strange sound and just start to use it more.

Good luck.