In the last fortnight we've suddenly been having a lot of pranks/unpleasant experiences with people on the other end of our door buzzer (we live in a block of flats so there's an intercom). We haven't been living here long but we never had this until now.
In the last 24 hours we've had: 3 rings (at 2am!) from a drunk bloke, 2 pranks this evening and, at 10, 2 rings from a different bloke (who was quite aggressive). This is London and the street is quite busy. We recently also had an attempted break-in by a group of teenagers and our flat was the only one targeted, despite being on the fourth floor...
I could ignore it if it wasn't for the fact that the buzzer is SO LOUD and obnoxious that it woke me (and everyone else in the house) up. Twice. 
We rent so we can't change the thing ourselves and there's no way to turn it off.
It's becoming a really unpleasant nuisance when you just want to do work/sleep through the night/watch a film. Help?