I have had this problem recently where my windy 750 starts cogging and making a clanking sound as it turns slowly. The first time it happened i dropped the tower checked the blade nut which is ok then removed the blades spun it by hand no problem then spun it with a drill still no problems. So i put it back together and let it fly. It has been a month and it started the same thing again. I wonder if one of the magnets has come loose and gets rubbing on the armeture as i have unplugged the mill from the complete system with no change in the generators action. The only other thing i can think of is a bad slip ring acting as a brake. I cannot get output readings as the turbine wont spin fast enough to charge Any ideas ?