I've had two of these ARFs (plus a kit version) and no radio problems. If not a direct radio hit maybe consider power line resonation or the like. I doubt the rudder cables were a factor unless you used a metal clevis on each end and a metal horn. Maybe invest in some rope for a tethered radio check. Vibration can show intermetent contact problems which otherwise go un-noticed until srash. What was the take off voltage of the flight pack? I did lose my first Ultimate to a battery failure. I do feel your pain, but simply put... There is a reason they call it the ULTIMATE. Get another if you believe you can.