Hello all, I am flying a Phantom 3 Professional and all of a sudden one of my motors feels a bit tighter than the rest. I normally check them before each flight and I went to fly yesterday and checked them and one feels tighter than the rest and it didn't before the previous flight. It was not crashed and the motor isn't dirty. Its spins smoothly it just feels a bit tighter. Maybe bad bearings? Are the bearings something easily changed? Thanks in Advance.