I think it is neccessary for us to point out that you are invalidating the products FCC/CE approval and that the responsibility for doing so lies with you. Therefore if it screws with any other electronics in your vehicle (bleeds onto your cellphone, reduces the range of your radio door locking etc) it's your problem not ours.

In practice, as Hugo says, it's probably still better (in terms of emmissions) than most homebrew MP3 players in the car.

Rob