Wheel balance vibrations can drive you crazy. In some cases a tire will balance perfectly on a machine and still vibrate on the car. It is a very common problem with Coker Tires. It seems that the tire is balanced in terms of weight but it flexes differently at different points as it rotates. It comes from poor quality construction, that's why it is common with Coker tires. To test for it, try rotating the front tires to the rear and see if anything changes. If you find a bad tire, you will have to replace it.