2002 pontiac sunfire grinding noise from the back

Hi, I have a 2002 Pontiac Sunfire and am experiencing a major issue. When I lightly brake I hear a grinding noise come from the rear of the vehicle
. Even when I turn the car off, I can still hear a noise, of something moving, come from the back of the car for about ten seconds.(It kind of sounds like someones in my trunk trying to get out, but that obviously, isn't the issue lol) I immediately checked the brakes/rotors, however, this is not the issue. I even replaced the motor mount, in high hopes that this somehow would stop the noise. It didn't. Please help!