Just put a new belt on it cause the old one was really bad and it still has the rattling sound but does not seem to hinder anythingm, I put 40 miles on today and no problems, but its one of those sounds that bugs me.
Well remove the belt and have a look at the primary, at the weights. If you need to remove the cover, remove 3 of the cover screws and find 3 more an inch longer and install them. Then remove the other bolts, last remove the longer ones. This will releive the spring presure!