Fantastic fan, a mind of its own ???

Our 5er is about 5 years old, awhile back the kitchen fantastic fan vent cover started going up and down on its own, it was suggested to me to clean the rain sensor, this worked great for about a year, now the same problem is back, I cut the power wire to the rain sensor on the hot side only and it still goes up and down at will, any ideas what to do next? If it would just work off the wall switch that would be great. Thanks