I have to disagree here, I'm no mechanic by any means but I have never had a problem like the one you described on this car in the 1 year I have been washing it......or any other car in my 20+ years of washing my cars.
It almost sounds like you have a caliber sticking or something.
I can't really say honestly but that can't be from just washing....not what you described. Take it to the dealer and have them look at it....still under warranty so nothing lost by taking it in.
Are your rotors hot when you wash the car and this happens?
Good luck