Our neighbours have taken to playing really bad music until 9:30pm exactly so we can't call the cops. I swear they watch for our car coming & only put it on when we're home. GRR!
Have you checked your local council laws on playing music and times? I was surprised when I looked ours up that music is not allowed to be played more than 10dB above background noise between 10pm and 8am on weekdays and 6pm and 8am on weekends. If their music is louder than 10dB on the border of their property or played after 6pm on weekends, we can call the police.

Every council is different, but I would check out what your laws say. I have been tempted to print out a copy of our noise pollution laws and leave it in a couple of our neighbours' letterboxes with the appropriate bits highlighted.