I've dealt with this several times over the years.
The switch is in a location where lots of dirt, french fry salt, you name it can get down into it. I have replaced this switch before, and I also have carefully taken them apart a few times, cleaned everything up and reassembled them, with great success. Some people would feel comfortable doing this, and some may not. If you can't fix it this way, they're not very expensive.
The switch does not have a buzzer, but it will buzz.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in