The voice of God vs the voice of Satan I listen to heavy music and I have had people tell me on numerous occasions the vocals sound like the voice of Satan, even when the band is clearly Christian (see For Today if you are curious). Movies tend to portray Satan with a raspy, scary, loud voice, but what does the bible say? And conversely, what does the bible say about the voice of God? Here are some verses I found:

Exodus 19:19 (NIV)


  As the sound of the trumpet grew louder and louder, Moses spoke and
  the voice of God answered him.


Deuteronomy 5:22 (NIV)


  These are the commandments the LORD proclaimed in a loud voice to your
  whole assembly there on the mountain from out of the fire...


1 Kings 19:12 (NIV)


  After the earthquake came a fire, but the LORD was not in the fire.
  And after the fire came a gentle whisper.


Job 37:2-5 (NIV)


  Listen! Listen to the roar of his voice, to the rumbling that comes
  from his mouth.  ... After that comes the sound of his roar; he
  thunders with his majestic voice.  When his voice resounds, he holds
  nothing back. God’s voice thunders in marvelous ways...


I couldn't find anything on the voice of Satan.

Is the voice of the devil ever described in the Word or is it something man made?
I think what you are seeing is a reaction to a stereotype created by our culture and the popular media.  Much like the picture in the minds of many people of the Devil parading around in red tights with a pitch fork.

In actual fact, scripture teaches us that Lucifer, whose name means "Light Bearer", was the "Morning Star" who fell from heaven in Isa 14 and Ezekiel 28 describes him as "the seal of perfection, Full of wisdom and perfect in beauty".  He is understood to have been an archangel and a prince of heavenly worship.  Other scripture teaches that he comes as an "angel of light" (2 Cor 11:14).

So, in actual fact, the devil is likely to present as someone visually and audibly beautiful.  Some allowance may need to be made for subsequent corruption after he fell, but since angels are purely spiritual beings, they likely can manifest in our realm in any form that serves their purpose.

Now, while I personally don't care for grungy metal and don't find it either pleasing or uplifting, I find it unlikely that it's inherently demonic simply because it uses raspy metallic vocals.