I started to feel a vibration through the steering wheel of my 2017 Impreza and pulled over to side of road, I placed my hand on the center of the left front wheel and it was much hotter than the two rear wheels, I then went to feel the right front wheel and it was too hot to touch. I replaced my front brake pads about 3 weeks prior to this happening and have only been doing short trips until now. I have removed my right caliper and removed the caliper piston to check the condition, it was like new all over except for a brown coloured mark about 1.5 inches long and 1/8" wide around the diameter at around the center of the piston. The only rust was on the brake pad side of the piston beyond the groove. Not sure what to look for next, any ideas would be appreciated Thanks.