I have a 2008 Nissan Altima Coupe 3.5 SE with 123k miles. To me, the rear rotors are telling me that the brakes are not working properly. I would expect to see three bands on the rear rotors: one band of rust at the top, a shiny metal band where the pads contact the rotors, and another band of rust at the bottom. As you can see from the pictures, this isn't the case. The top picture is the driver's side, the bottom picture is the passenger's side. I've previously replaced the rotors and pads as well as the passenger's side rear rotor. Do I have a second bad rotor?
You have seized pads or a seized caliper. Or, you installed low quality pads where the backing plate has rusted and buckled the friction material and possible broken it off. Remove the caliper and check for free movement of the slide pins. If they're corroded, you can replace just the bracket and pins sometimes, depending on design. Then buy new high quality rotors and premium name brand brake pads, preferably with galvanized (not painted) steel backing plates. See this youtube video on NRS pads. Also watch this Chris Fix Video. And this post for how to buy brake pads