Brake Disc Pads problems of the 2015 Infiniti Q50

When the car had 8k miles on it, the front rotors went bad I. E. Defected and Infiniti dealer fixed them and replaced the front pads as a warranty item. Now at under 24k miles, the rear breaks are gone bad but the dealer and Infiniti corp. Are denying they're defected and refuse to fix them. This is my 3rd Infiniti, I had before a 2008 g35s, and 2013 g37s, I drive my car regularly in town and highway, no excessive driving, and my rear brakes never went bad on other Infiniti cars under 24k miles. I believe the rear breaks have problems just like the front ones did and the dealer considered them defected rotors basically and fixed them as a warranty item. The dealer recommended me to replace them few weeks ago when the car was in the shop for some electrical problem, but the breaks didn't make any noise at the time and I thought the dealer just wants to make some money. But, starting yesterday I heard the grinding sound and that's when I called the dealer back and also talked to Infiniti consumer affair, and they refused to cover them.