Those cheeks on all models vibrate. Its due to engine and prop imbalance. It usually goes away at about 1/3rd throttle once the motor is running smoothly in its powerband, wel the frequency has just changed to a higher one where your eye can;t see it.

Removing the cheels and fitting a cowl is the best option, but the cowl is a rare beast indeed. I hve one on back order from TH since May. Only expecting it end June but more than likley end July.

You can also fit silicone rubber between the engine mount and the fire wall to damp the vibration.</p>