[landrovered]

Those are anti rattle / anti vibration disks, they are likely stuck to the back of the pad. Take a putty knife and slide it between the back of the pad and the disk on the anti rattle device and it should seperate allowing you to remove the pads.

This is what they look like http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=996-352-086-00-M260&catalog_description=Rear%20Brake%20Pad%20Vibration %20Damper%20%2D%20Round%2C%20%33%30mm%2C%20%28%34% 20per%20car%2C%20sold%20individually%29%2C%20Boxst er%20S%20%28%32%30%30%30%2D%30%34%29%2C%20Each%20% 20