I just recently adjusted my belt tension, since then at a specific speed (20-10 mph) I have a harmonic noise that I can only contribute to the belt. It sounds a lot like a rear brake noise, but I have ruled that out.
ride the bike and at 60 or so take hands off bars. If bike goes straight for a bit your belt is aliened. If it quickly goes left or right then its not aliened.
Your sound could be from your fuel bodes maybe they need cleaning or you have a air leak maybe even exhaust leak.
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