I don't think it should be audible while rolling E. If it's up on the stand and you hear it drag, that would be within expectations, but not while the motor is on and riding. I cleaned my calipers with brake cleaner and the pistons wouldn't retract for shit after. Spun the wheel on the stand and it wouldn't go more than 1 revolution. I swapped calipers and now it'll spin ~3 times before stopping. Again, if you can hear it while riding, I'd say you have a bit of an issue.