I am presently having the same kind of issue. I think I've pretty much figured that mine is a bad servo. The servo on the rear right side from tail in twitches in flight. At first I thought it was interference, but then I disconnected the motor and it would still do it, so I swaped that servo, which I think is channel two if I remember off the top of my head, and i switched it with servo one. The servo in the rear right position would still twitch even though it was plugged into a different channel. That's how I figured it wasn't the receiver or interference, but is most likely the servo. Tower has a deal where you can get 3 hs55's for 31 bucks, I'm gona see if my hobby shop will match this and see if I can't get some servo's or something.

I don't really understand it though, because I have only crashed my chopper 2 times. the first one resulted in a boom strike and a bent spindle, and the second one just resulted in a broken set of blades and I straightend the main shaft, so I don't understand what the deal is and why that servo would be broken. Maybe it hit it just right, or maybe it is a QC issue, who knows.