I encountered this twice before and they are right, it is the brake pad that needs replacing. The first time I bought the car and didn't know the status of the brakes, drove it around for a month and then let my sister drive it. Well she takes off down the road with the E-Brake still on for almost a mile until I finally recognize it and get pissed. After that incident, I noticed the grinding while in reverse. I could even let it coast backwards down a hill and still hear it (without even pressing on the brake). After I got the pads replaced, I went another year until I let her drive the car again. But lo and behold, the same event happened and she drove with the E-Brake on and I got the same grinding noise. Boom, another chunck of change down the drain for more rear brake pads.
As a rule, she can no longer drive my car