I have a Phantom 4 that has developed a strange quirk. When manually landing in normal mode, the aircraft will go into an uncommanded climb approx one foot from the ground climb two feet start responding to the controller's down command then repeat. It's already resulted with the aircraft striking the ground and overturning during a manual landing from the aircraft not responding. I've started using ATTI for takeoff and landings. Is this an issue with the sensors and should it be in the flight log? I can put it in a two foot hover and watch it go up and down on its own. Any help would be appreciated.