Bernie,
From what I can find out it is holes drilled in every milled section. Will try and find out more and post reply. Not sure why yours does not make any noise unless it has holes drilled. Mine is well worn and can be heard in the cabin easily. Other possibility is worn belt (ie square sections have too much slack and air not getting trapped.) or incorrent belt as "ebustin" suggested?
Anyway will try and find out more.
PS. They must have run out of moonshine over there into kerosene now??????
TC