Riding in Cars with Music

I have some questions for all my wonder-full readers!
I would like to know your perspective on:
etiquette involving riding in someone else's car.

     When carpooling with an acquaintance, when is it proper to ask your acquaintance to change and/or turn off his/her music? 

Is it ever polite to do so?
Should you say something only if the music is explicitly offensive to the other passengers (e.g. listening to heavy metal while children are in the car)?
What if you and the driver are involved in a serious conversation which you cannot concentrate on due to the throbbing base?

What if you were in a car with four non-Christians, and rap with infamously crude language is playing? Would you not say anything to keep from being a holier-than-thou snob, or would you make it known that you don't approve of that kind of language because you are a Christian -- so that your fellow passengers will know your beliefs are also you lifestyle? 

 Have you ever been in a situation in which you did (or wanted to) ask the driver to listen to something else?
What did you do?
If you haven't experienced this, what would you do if faced with music that you simply could not stand?

Inquiring minds want to know.
Your curious friend,
Hayley

P. S.

I have been in people's cars before. It's simply amazing how much one can learn about a person by riding in his/her car.

The first time I rode with someone who played yucky, immoral music, I was shocked -- not because of the music but because I had entertained a completely different idea of who that person was than the idea I was getting in her car.

Another time, I wasn't shocked about the music or the person; however, a new Christian was in the car with us, and I was ashamed that she was the one who stood up for morality and manners when she said it was an inappropriate song for mixed company.

After that, I had determined to not let such an opportunity pass me by again. When I found myself in another car with young Christians and a substantially worse song came on the radio, a couple of other passengers expressed their surprise at the horrid expressions; but the driver did not change the station. So I spoke up, and the radio station was changed. (I actually was shocked by the song, as opposed to the other two times I described.)

I don't think it worked out the way it should have. But life doesn't work out the way it should, either.