max iv loud clutch at idle?

[mopard3]

Hi, I have an 02 max 4 18hp briggs. When the machine is at idle the clutch on the motor is making a clunking/knocking sound. When I bring the idle up a small amount the noise goes away. I don't remember it doing this before but I have not used the machine much since I got it. Does this sound normal?? thanks!