Did you buy the car from Nissan? I'm not sure about returning the pads but the dealership should be able to help you. Or atleast check it and tell you what to do(since the pads are new).
the pads are NEW....but in the groove on all of them there was brake pad material built up. i had to clean the grooves on all the pads to remove this HARD material. After that, the noise was gone....for about 2 days.