Tire Bulge problems of the 2008 Mercedes Benz C300

Approximately 2 weeks ago I received a message on my dash board to correct the tire pressure in my new 2008 Mercedes Benz C300 with less than 4000 miles. I inspected the tires and noticed a bulge in the sidewall of the rear tire on the passenger side of the car. I called the dealer and was told that it wasn't covered under warranty and I have to purchase a new tire, which I did. Now approx 2 weeks later, I have a bulge in the sidewall of the front tire on the passenger side of the car. The tires continental contiprocontact 225/45 r17 91h cost approx $280 each to replace at the dealer. This has got to be a defect from the tire company. Tire brand: continental tire line: contipro contact tire size: 225/45 r17 91h component: sidewall bulge dot code: lm7r pxh6 3707 tire was mounted 2008 Mercedes Benz C300 4 door.