If your ISP is like mine, I called and ask why my cable connection was so slow. Well here is my answer they gave me...... When you are on a cable connection, you are sharing Bandwidth and when you are downloading mp3's you are using a lot of Bandwidth. My cable company has restricted the amount of bandwidth users use on certain ports where mp3's are downloaded. So that is probably why your downloads are slow.
I am unhappy that it is not fast but the good news is I can still download but slow. Some people are blocked altogether.
You might want to call your ISP and ask them is this true in your case. They can just say yes or no. Hope this enlighten your concern.