something like that also happened to me 2 times, on the front passenger wheel.
first time, my bearing was loose making the brake to always brake, so it also cost me a disc brake and brake pads. the sound was extremely awful when I used to turn.
second time, my mud flap lost 1 screw and the wheel touched it depending of the curves and bumps of the road. all I did was to put another screw in, it took me a while to notice it, because when we look at the wheel we can't notice it, I just noticed it when I changed my wheels for winter.
so you look like you're having the same problem as my first time.
