Yesterday I noticed some strange behaviour -the drone was bouncing up and down at about 50cm off the ground, and randomly drifting (both when there is no stick input, in GPS and ATTI mode) After witnessing this, I landed the drone, and noticed that one of the propellors seemed to be spinning slower than the others, and there was a slow oscillating whir that I hadn't heard before. Is this a damaged motor/bearings? Would that be the cause of the drift/bouncing? I have also updated to the latest firmware and have done calibrations - other users have reported that this has caused issues with drifting.