The problem with hip-hop and rap noise isnt the form or the rythmns or anything else like that. In my opinion it most certainly CAN be used for godly puposes if it is used in a godly way and manner.
But when I see rap and hip hop noise being used for godly purposes the ones involved sound like goons and thugs, they look like goons and thugs, they lurch around like goons and thugs and the you cant understand anything they are saying. A good message with the gospel included is utterly worthless if the message can not be understood plainly.
At that point they become instruments of the evil one for sowing confusion and chaos rather then truth and the clear gospel.
And its not just rap and hip hop noise. I've heard the same chaos and confusion with some of the harder rock groups that some young christians enjoy.
The point of any gospel music is to deliver a godly message, not deliver a goonish, thugish, unintelligable chaotic message.
If I ever see a gospel rap group, or hard rock group, behaving and looking like like christians, and delivering their message in a godly and civilized manner, I'll joyfully give them the "thumbs up" and support them enthusiastically.
Mike