you can only hear it because your pipes are to quiet

I’m thinking new belts make that noise whereas old belts, worn in, make less noise.

Could it be too tight?

I ran an open 3" belt primary, on a kick start only, shovel head , for years with an old Hub clutch, so you get that noise & the bucket of bolts noise. every time you pull the clutch in. some said drilling holes in the toothed belt drive could lessen the noise. just make sure its running true. & you have the inside & outside covered to stop stones getting between belt and the drive teeth. And will virtualy last forever. my shovel with new owner still runing that but with modern style clutch. good luck with it! 

sweet! just make sure, the inner part has a cover like that too. but plenty used to ride with nothing covering inner or out. and never worried. just blue metal between belt and tooth drive & the stone will put a hole in the belt. I made the inner cover from plate alloy.