mine did this, I checked the servo's and I had one that was going insane (the collective)

for that holding the heli by the skids, it was a great idea that I used until that fateful morning when it bit me in the ass.. I was holding the heli, gave it throttle, nothing happened.. gave it full stick, nothing happend... then I moved it back to zero and SOMEthing happned.. the rotors proceeded to take three chunks of flesh out of my nipple.... obviously thinking back, I had the throttle reversed, full stick armed it, and shutting it down opened it up.. just be aware of what you are doing!