Actually music does make a difference. I used to listen to (and enjoy) heavy metal when I far from Christ but then put it away when I was back in the arms of my loving Father.
I have never seen an on-fire-for-Jesus Christian who is a heavy metal artist or even a heavy metal fan. It seems a good number of the bands are so compromised and lukewarm that crossovers are to expected and even outrageous scandal is not far away from expectation. I consider this music to be a "weight" and not a sin--similar to some other forms of secular music or television. The problem is that you are what you eat. If you are eating cake and McDonalds every day then I'm not likely to see you at the marathon the next day (or at least not doing very well at it).
This is not a salvation issue. It is a maturity issue, I think. There are many things that I have put away since coming to know Christ. I stopped caring about what brand of clothes I wear. Today I hardly wear anything that says anything on it and if it does, it's usually something about Jesus. I stopped listening to secular music. I stopped reading Game of Thrones (and even worse, watching Game of Thrones). Some things are going to slow you down in your race. If you are not willing to put them away then the question has to be asked: Are you really serious about following Jesus, or are you more serious about getting your kicks and your comfort in life? I've asked myself this very same question and it has led to me putting many things away. And, I am sure, there is still more to come because I love Jesus.
Here's a quote from a great preacher, Tim Conway:
"I want us to be serious about this race. So
what are the things that tend to weigh us down? What are the things that tend to help?
What are the things that tend to hurt? What are the things that hold us back? What is it that
distracts us? I mean anything, that is going to slow us down. Remember, we have to keep is
in our minds all the time. What is the nature of the race? The race is: A Race of Faith. That
means trusting and holding on, not giving place to deception, not giving place to worldliness.
Focused on Christ, yearning for Christ, loving Christ, running for Christ, serving Christ. For
the glory of God. Our eyes set there, our eyes beholding Christ. As we fix our eyes on Christ.
It's though He's at the finish line with His arms wide open. We're running, we're pressing
towards that prize. We're reaching forward, straining every fiber, every nerve. You do not
want the things in your life that tend to make you spiritually sluggish. You don't. What is it that takes your
mind off of being Godward? We are to set our minds on things above (Col. 3:2). What is it
that gets your minds on things below? You know what those things are. We know the things
that tend to make us worldly. We know the things that tend to make us not want to run."