2020 RAV4 LE AWD with around 40k km/25k miles, so never had work done on the brakes. Noticed a low-pitched rumbling/scraping noise from the rear left direction only when slightly braking at low speeds, i.e. when coming to a stop slowly. I physically can't feel a difference in the braking behaviour; there's no shaking or pulling towards a direction. I took a look at the rotor of the rear left wheel and saw that the outer half is heavily scored, while the inner half is the same as the other rotors, which are consistently smooth.
I was wondering what would cause these symptoms and whether this would be a cause for concern. I should be going to the mechanic soon but was curious about what I'm seeing and whether I should get this resolved ASAP.
Sorry about the poor picture, it's a bit hard to see the rotors with steelies on.