MY 1982 Honda CB750K is making a strange noise when the clutch is let out. The noise sounds like a slapping or clunking. It doesn't make the noise when the bike is cold or when I pull the clutch in. I first noticed it when it was idling in neutral after a 30 minute ride but have since realized it seems to be making the noise while going down the road too. Does anybody know what the problem is and how to fix it?