I'm experiencing rotor rub in both my front and rear brakes. This will only occur when wet. So for example after adjusting the caliper by loosening the mount bolts pulling the brake and tightening I can eliminate all rotor rub. If I splash some water on the caliper or rotor they start to rub/grind. Why does this happen?
I have notice the same phenomenon. If you keep washing with clean water the rubbing noise should go away. My best guess is that the water coming off the tires and falling into the brakes brings a fine road grit into the system. This coats the pads/rotors reducing tolerances, causing rubbing to be more noticeable.
If it is really wet for a long time, the rubbing will accelerate pad wear (which I found out during an insanely wet Dec last year).