I've pulled open microwaves and removed the buzzer. My flatmate thought I was nuts at the time but as a person often up late reheating things it's a considerate thing to do, there's no need for a device where you can't turn off the sound. Even worse when it continues making noises every 30 seconds afterwards until you open the door. RIP anyone who likes to cook then cool.

Microwaves are already loud appliances, I can hear it running from the next room. Meanwhile you'll be hard-pressed to find a toaster that beeps.