Asofel, I just finished reading "Driven to Distraction" by Hallowel and Ratey and it talks about how people with add often need/crave constant mental stimulation and I think music would certainly be one way of getting this.
Have you read the coping with ADD thread in this forum (started by Zee Justin)? I have never been diagnosed but I read that thread, ordered Driven to Distraction and was like "Holy [censored] that's me!" Might be something to look into.
Obv I am not a doctor and this is wild speculation since I don't know you. , but if you have joked about it with friends and had a teacher ask you before it's definitely a possibility. I don't think standardized tests are a good diagnostic tool because most people with add are naturaly quite intelligent and can usually do well on such tests just by winging it.
edit: thread was not started by ZJ but here it is.
add thread