I know this thread is 2 years old and the OP is probably not coming back since he is recovering from stab wounds from mustering up the courage to tell his neighbors to turn their rap music down (in that case, my advice is to move away from your ms-13 neighbors)... So I'll make a general comment:
Are YOU my neighbor? lol, I play rap (or whatever floats my boat) loudly. In fact, I'm playing stuff right now... It's 1 am, but I guess it's not blasting.
I actually wouldn't call the cops,
maybe I might have mentioned something to them if it was intrusive to my kid's sleep, but he's grown up. I'd be more pissed if they blocked the driveway or something...Always be the adult and give the person a chance to correct the behavior on their own.
Wait? is it old school, golden age stuff or the BS that passes for rap today? If it's new stuff, call the cops and say you overheard them talking about "mailing the anthrax envelopes to the orphanages and hospitals". SWAT will kick the door in and beat the crap out of them.
If it's golden age (NAS, KRS1, Gangstarr, etc), cut them a break. They are only human.