Sometimes when my friends/colleagues (2-3 people) and I travel by train there is another group of people who play songs on their mobile phones without using headphones and on full volume.
Many of us (as well as other passengers) get disturbed by the loud music, however, they are a large group of people (around 5-6 people), so we can't be rude towards them in order to get them to stop.
So, how can we ask them to stop the music, without making a problem or being rude?
At the moment, we move to another place on the train or sometimes, in retaliation, we play music even louder than their music (this is not a solution but we are doing so only to disturb them as they disturb us).