one of my motors feels different from the other 3. It's my RR motor. When I spin it by hand there is one rough spot. It doesn't feel right. It feels like a mechanical bind. don't go telling me to oil my bearings - I've seen that thread and I won't fall for that one. haha My quad is less than a year old, I bought it last March. I think I have around 400-500 flights on it. Most are pretty short duration, 5 to 10 minutes. should I be concerned? Should I replace it? My gut instinct tells me it would be better to replace all 4 motors at the same time. Is that wrong? then I would keep 3 used motors as spares and trash or take apart the rough motor.