Do you have run-flats?
I have had three of my four replaced since I got the car in march. The last one was for a puncture in the right rear. Shimmies like crazy. Took the car to Turner for service and asked them to check the balance on the wheels once again. Their finding was crappy tires. Wheel without the tire rotates true. Wheel with the tire wobbles and is the source of the shimmy.
Just a thought