Tire Bubble problems of the 2004 Chevrolet Colorado

The contact owns a 2004 Chevrolet Colorado equipped with cooper cobra g/t radial tires, tire size p255/70/15. The contact was driving approximately 35 mph and the vehicle began to vibrate. The vehicle was taken to a tire center where they informed that the rear passenger side tire tread belt exhibited bubbling. The tire was replaced. There was a recall under NHTSA campaign id number 06t016000 (tires:tread/belt). The dot number was not included in the recall. Recently, the front passenger side tire tread exhibited a similar defect. The contact was in the process of replacing the tire. The failure mileage was 69,000.