The OP asks: "Is it a sin for a Christian to listen to Heavy Metal music?"
ha ha ha.
I could see a person walking through a store, which has this Music playing.
Then, God sneers down, and delcares that every Customer has just sinned.
I chuckle at the "loose" logic of the OP: "Seeing as how some heavy metal music as unChristian and ... is it a sin for a Christian to listen to [ANY] heavy metal music?"
So,
1) Some songs are (in the OP's imagination) un-Christian;
2) therefore, ALL music should be sin-ful.
Give me a break.
Please, OP, list some of these so-called un-Christian songs.
Stereotyping at its worst (and lowest).
I ask the OP, is this ALSO True (in your warped perspective)? ... Some Muslims are terrorists, therefore, ALL Muslims are EVIL.