my 650's drive shaft made a bit of noise that could have been described as whirring. It didn't sound problematic, just mechanical stuff operating. Have you had a tire replaced or repaired recently or some reason for drive shaft to have been disconnected?
May not be helpful, but these are the things that came to mind:
Final drive oil level low? Everything tight back there? Rear wheel alignment hasn't slipped out a little that might cause a little strain?
Sorry couldn't be more helpful.
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