Its possible to be the reciever, but could be a whole list of items. I'd try moveing things or pokeing around with the motor not running to see if you can instigate & or isolate the problem. You stated it only happens once the throttle is over 1/2 open, so im guessing it is vibration induced. Can you bypass the switch & plug the battery directly into the reciever, that will rule out the switch. Then try un plugging one servo at a time, looking for bad connection on servo extension. Try replaceing the reciever if you can, i have had loose Xtals, broken antenna wires, even cracked ckt boards on my helicopter recievers from previous crashes. You'll have to become a detective, but at least you decided not to fly until you find it, since it wont heal itsef in the air You'll eventually find it & please let us know what you find.....Gene