Our 7720 started making noise on the cyl. drive at idle speed. When you go full throttle it goes away. The electric hdr. drive clutch also wants to creep alittle when itis shut off. Can't find any bad bearings or anything that would cause this. Yesterday late the v.s. belt for the cyl. drive broke. I'm wondering if it was bad causing the vib. or it broke because of some other problem. Any suggestions ?? Thanks,Paul