I gave up.

At 10 pm I asked him to turn it down. At midnight I asked if I could please stop listening to it now, and offered him my spare headphones. At 12:30 I called the police non-emergency line. The lady heard the music over the phone, and agreed it was definitely excessive. I told them about him drinking in the vehicle too. Hopefully the cops aren't too busy tonight, and actually have time to deal with this. *sigh*