Just bought an '03 z06. It has a cyclical vibration starting at 50 mph and on up. I bought new Goodyear super car tires all around. I had the tires balanced twice at the Goodyear dealer and once at a hot stuff tire place for an additional $40.00. It drives just fine and has no vibration in the wheel. All of the vibration is felt in your feet on the floor or in your seat. I had the rear axle serviced. Any help. It drives me crazy.