This is something that really makes me mad.
Much as I love music, I really do not want to hear the racket from other people on the bus. That dreadful "Tsk Tsk keecha" sound from other people's music bugs me no end.
It's really annoying. These gadgets have earphones or headsets so they must be using it. It be considered bragging having to play music loudly while in public transport. Loud cellphone alerts are already annoying so this action is worse for me.