There are sooooo many things that can cause vibrations/harmonics. The only fix is hands on everything. Slingers might be a drive boss wear issue or loose flywheel, worn ramp plate. (Just guessing here) Vibration could start anywhere on the scoot. Even a loose fuel tank. Bottom line is take it apart, and inspect everything.
Scuzz, W/ the scoot on the center stand try to move the engine by twisting, pulling, pushing the rear wheel. You may find something that way. It will take some force but ANY movement is too much.