ORIGINAL: mr502go
Did you use foam tape to mount the gyro?? Futaba sells the stuff I think you usually get three squares of tape per package, stack all 3 and mount your 401 with that stuff, it helps damp vibrations, and keeps from "confusing" the gyro.
You only use 1 square to mount the gyro with. If you're using 3M outdoor mounting tape, which works well, better than the stock foam really, then use two layers.