I just go through putting a new gearbox, main bearings & seals and bottom protector cups on my RCK60P-21Z mowing deck. When I engage the blades I get a scratch noise about 1 1/2 seconds apart. Blades are indexed properly and tight. New cups under deck seem to be running smoothly. Noise is very regular and consistent, like a beat to music. Please help me if this has happened to you or if you have seen a previous thread?