I am having the same problem, but I have the Stock OEM M-sport rims. My car has had this vibration from day one. They replaced the front drivers tire, and both rear tires 'cause they couldn't road force balance them. That was at 400 miles. I now have 1,350 miles and I still have a slight shake coming from my rear right side of the car. happens around 65mph - 75mph and I can see my passenger seat wobble back and forth and can feel it in my drivers seat and slightly under the car as if it hops around those speeds.
I am taking the car back in again to the dealership Monday morning, would anyone else know what the 'cause of this would be?