Well it's mainly only in reverse, sounds like front brakes but haven't changed the brakes since I bought it. Only 55,000 miles. Should I get new rotors or pads?
Please take a picture for us of the front pad, as well the back pad. then we can say.
Your front pads are where the sensors are now hitting, giving the warning by sound, not visual. It is best to get to a dealer or parts shop, and get some replacements, and change out your fronts for now. Your reap pads are no where near the wear line, due to the rear not doing the braking , or the park brake, used. One is for the park brake the other for the actual brake.
Fronts always wear out first, not true. Front disk and rear drums, front will always wear out.
fronts and rear disk brakes all wear evenly, many do not believe that, I do!
I do not think your rotors are shot, are they warped? really messed up in finger print, or you are riding the pads to the back metal plates??