Yeah, I like some Metallica songs too. However, some of their songs are evil, written in the first person, as if Satan himself were talking. Some of that came from a time and an age when Death Metal was cool and people flashed Satan/rock signs. I can’t be sure, but I don’t think Metallica worships the devil. Most groups of that time played dress up (like Kiss) and acted evil for effect. Metallica mellowed a bit as they got older.

Rock and Satan have long been associated together. Witness the popularity of Guitar Hero. The girls have horns, while a Satan prop dances around in the back. It’s all tongue in cheek.

You create problems in your mind by pondering evil all of the time. It opens the door to Satan.

“In your anger do not sin”: Do not let the sun go down while you are still angry, and do not give the devil a foothold. Ephesians 4:26-27

So instead of immersing your brain in evil all of the time (Metallica and other things), God wants us to think about good. Close the door to evil and let God in instead.