Every couple years somebody in our area will do something ridiculous . . . like park 30 cars in the middle of a street with subwoofers blasting music at 11:00pm, or like hold a wedding celebration with two drummers wailing away at midnight on a work night.
My approach:
- Take a deep breath, calm yourself down and remember that they're not purposely trying to be assholes. This is an important step.
- Head over and talk to whoever looks like he's in charge. Be reasonable (firm but friendly), explain that it's too loud and you would really appreciate it if they would keep things down.
- If they don't turn it down, or if the music gets louder half an hour later, call the police. (In your case it would be the building manager I guess.)
I've found that by and large people are reasonable, and you rarely need to escalate to the third option.