First thing is to work out where exactly the noise is coming from. The motor, the barrel where the clay is, for the gear box. If it's the motor but still working and not getting too hot (they do tend to run quite hot anyway) then I'd just leave it unless it's really screaming to be put out of it's misery. If it's the gear box then try changing the oil. It's it's in the clay barrel then you need to strip that area down, clean out, and see what's making the noise- maybe time to change a bearing. Good luck