Hello all. Had my Phantom2 for a few weeks now, very impressive. However on the first test flight with the ground station it crashed, fell about 3 mtrs and landed on one of the rotor arms. It's slightly bent but managed to straighten it. Started it all up, green lights, no problems. Started to fly all was ok and it started to vibrate with a 'whistling' noise. When I lightly take hold of the landing gear whilst it's flying the vibration stops, but then returns shortly after. I stripped it down, remade all the connections. I ran the motors at full speed in both directions, the all run fine, there is no vibration and they all run true. Took it for a test flight, all ok but after about 2 minutes the same symptoms returned. About to strip it down again. I've checked it with the DJI Assistant software, no error messages, no need for any re-calibrations, it says it's fine. Has anyone else experienced this? Any solutions or ideas more than welcome. Thanks in advance.