One of the things this newbie learned from this site is to check to make sure the motors spin/ turn freely before each flight. Mine have always turned freely, but now one is different than the other three. When I spin the propellers during my preflight check, three spin all the way around about 2 times before stopping, but one now will only spin 1/2 a turn. Wasn't sure how significant that is. At what point does it become a problem? I don't feel any binding or grinding or anything else abnormal. I completed my preflight check and took off. Everything seemed normal, but after doing some flight training exercises, when I shut off the motors, the one propeller stopped long before the other three stopped. Any recommendations? Thanks!