CVT gearbox vibrates when in drive on slow acceleration

More then likely this is not a CV joint issue but an issue with the steal belt inside the CVT transmission.

The way these work is there is a steal belt that connects two pulleys and as you accelerate one pulley is changed in diameter and that changes your ratio so that you can speed up and not have any shifting.

What is most likely happening is the belt is slipping and you are feeling that as a vibration. When you put it in S mode the pulleys actually lock in and change their activation points. So it is not allowing the belt to slip.

I would suggest starting with checking the fluid. I attached the process below. It says this is for a CVT but it looks like the auto transmission. Either way, I would suggest changing the fluid in it and go from there.