Scoring on brake rotor hat

Hello all,

I have a 2010 Hyundai Sonata which I recently did some brake work on. I replaced the rear brake pads but not the rotors, which were fine. I decided to take a look at the front brakes as well and found that I will have to replace the front pads very soon, because on the passenger side, the inner pad is much more worn than the outer one, which tells me that I most likely have a sticking piston. I am comfortable with that and plan to change the caliper. However, while spinning that rotor, I noticed a metallic grinding sound. A closer look showed me that there was a fresh score mark on the side of the 'rotor hat' that seemed to indicate that the hat was out of round as the score mark only showed for about a quarter of the circumference. I'm not sure if the problem is contact with the caliper bracket or the brake pad, not that it matters. There is no brake pulsation, only a mild grinding at slow speeds when the brake is applied, and no, it is not from the braking surface of the rotors ... they are fine, though I am leaning towards changing out the rotors , just to be on the safe side. I find it interesting that the hat can be out of round without a corresponding effect on braking action.
My question is: Has anyone seen anything like this before? If so, what could cause it? Overheated brakes, maybe? Any ideas?

 

The slider pins are likely sticking, not the piston.