Oh MAN tl;dr. Even as a Christian, some of my favorite bands are Pagan's Mind, Lamb of God, and Scar Symmetry. Some very non-christian bands. It affected me once long ago, but I've been able to not let it affect me. If this is something that you think will be a problem, your best bet is to either avoid it, or combat it with christian-infused messages. Think of the secular music as propaganda - that you must fight with your own counter-propaganda.