Why do microwaves beep?

Our microwave oven is very noisy. When its on, it sounds like a vacuum cleaner on heat. Are they meant to be that loud? Is anyone elses microwave like that?
I wouldnt care, but Joe likes to microwave at least 3 things for breakkie very early in the morning and it wakes me up. Not so much the amplified helicopter sound, but the huuuuge long beep that it does when its finished. BEEEEEEEEPPPPP. Why does it do that! Kettles dont beep to tell you they've finished. Nor do toasters. Or dishwashers.....
[dino]