While I had my XJ550 apart installing my new clutch I decided to address a known problem with many bikes of the same era. It seems the oil pump gear on the back of the clutch basket has free play from the dowel pin that secures it from rotating. This small amount of play transfers into clutch rattle noise. On my CB750 this noise was especially loud and annoying as hell. Simply remove the gear and press part of a roll pin around the protruding section of the dowel, reassemble, done. You'll notice the chugging noise these bikes make at idle has greatly reduced, you'll still have some, it was the gear on the back of the clutch basket chugging back and forth.