2009 Volvo C30 Tires & Wheels Problems

RECENTLY I HAVE BEEN EXPERIENCING INTERMITTENT VIBRATIONS WHILE DRIVING. I HAD THE CAR INSPECTED AT AN INDEPENDENT TIRE SHOP WHO FOUND TWO OUT OF FOUR TIRES (ONE FRONT, ONE REAR) WERE OUT-OF-ROUND BECAUSE OF TREAD SEPARATION OR BELT SLIPPING. I BEGAN TO SUSPECT THAT THIS WAS RELATED TO VIBRATIONS THAT I EXPERIENCED EARLY AFTER BUYING THE CAR USED WITH NEW CONTINENTAL DWS TIRES INSTALLED, FROM A VOLVO DEALER, JUST OVER TWO YEARS AGO. THEN I HAD ASSUMED THAT THE PROBLEM WAS A SLIGHT IMBALANCE OR POOR WHEEL MOUNTING. I HAD THE CAR INSPECTED AT A CONTINENTAL TIRE DEALER TO INITIATE A WARRANTY CLAIM, BECAUSE THE TIRES WERE POSSIBLY UNSAFE TO USE AFTER 2 YEARS AND 18000 MILES (WELL WITHIN THE 6 YEAR WORKMANSHIP, AND 50000 MILE TREADWEAR WARRANTY). THEY FOUND UNEVEN CAMBER WEAR AND CUPPING, BUT NO TREAD SEPARATION, AND THE CARS SUSPENSION AND ALIGNMENT CHECKED OUT. CONTINENTAL REFUSED TO HONOR THE DEFECT IN WORKMANSHIP WARRANTY CLAIMING THAT I HAD NOT MAINTAINED THE TIRES BECAUSE I HAD FOLLOWED THE CARS MANUFACTURES SERVICE RECOMMENDATION OF NOT ROTATING TIRES (SACRIFICING TREADWEAR FOR IMPROVED HANDLING). I RECONTACTED CONTINENTAL WHEN THE LEVEL OF THE VIBRATIONS AND THUMPING NOISES SUBSIDED AGAIN BECAUSE AN INTERMITTENT VIBRATION COULD NOT BE EXPLAINED BY CUPPING AND CAMBER WEAR BECAUSE THEY ARE PERMANENT, THUS SUPPORTING THE INDEPENDENT SHOPS CLAIM THAT THERE IS AN INTERNAL DEFECT IN THE TIRE ALLOWING THE BELTS TO SHIFT. CONTINENTAL HAS DISMISSED THIS AS A POSSIBLE CAUSE AND IS SEEMINGLY IGNORING THE FACT THAT THESE TIRES COULD HAVE A POTENTIALLY DANGEROUS MANUFACTURING DEFECT.