Why do old men hum?

[spazvas]

This may seem a strange question but have you noticed that men over a certain age have an annoying habit of humming?
It may seem faintly amusing, but I tell you what I am slowly but surely going round the bend cos I have one sitting next to me at work and he does,nt stop humming or talking to himself ALL day.
My nerves are getting pretty shattered and I almost dread coming into work now and I used to love my job. I wear earphones all day and this is doing my head in too.

Please HELP what can I do?!!!!

[coccinelle]

Have you tried humming louder than him? They usually look at you as if you're nuts, when you do this!