Metallic rubbing, that sounds like you need new pads. Mine lasted about 6,800 miles. I had never touched brake pads, but it's not very hard to change them. I flushed the brake fluid at the same time.
If they have worn unevenly, you may also need a little silicone grease on the guide pins - read all about it here:
http://www.gz250bike.com/forum/viewt...p=36774#p36774