I think it is an act of aggression personally. Almost dearing you to tell them to turn it off. They are aware of there surroundings as well. i.e If a bus was full of Peckham Boys then non-Peckham boys would not have the urge to play the music loud, if at all

I would say that in my expereince 9/10 the perpetartors are black but I will concur with Kunjufu that it is a youth problem cos I post in forums where they complain about the trend in Newcastle, etc