I have a shimmy, or pulsation - wouldn't really call it vibration - in my car and I don't know where to start. When going 10-15mph it feels as though the car is bouncing up and down, like the road is uneven. The faster you go, the headrests and visors can be seen shaking. It's akin to the feeling a bent wheel gives you. It's a Starmark-certified car with new Conti's, and I just had nearly the entire front suspension - minus shocks and springs - replaced for squeaks. They rotated and balanced the tires when they did this, and it hasn't changed. I'd like to think they wouldnt sell the car with a bent wheel, especially considering it has new tires and they have now been on the balancer twice. I've read about rear diffs and flex disks. Any ideas that I can use when I take it to the dealer? TIA.