Sorry for the mental lapse. I can only give a few guesses, Perhaps the brake cable when taught is hitting a panel, or the frame. Maybe the belt "flapping" inside the cvt. If you are sitting still, can you make it happen each time you apply the rear brake? If so I would have someone else apply the brake, and inspect/ touch everything involved. I am thinking you have a harmonic problem more than a mechanical prob. If the scoot is DEAD still, there is nothing I know of that ties the brake to the engine that would create a drain on the engine running. If the scoot has to roll SLIGHTLY to create the symptom, perhaps you have a bad return spring in the clutch. This would give a slight shudder upon stopping!
