When I set up my FC Roll and Pitch inputs from my flight controller I can get everything to monitor and show proper activity until I turn on the gimbal motors. Then on the monitoring page I see the EXT_FC_Roll and Pitch jumping all over the place.

This seems to only happen while running the Gimbal power from my Power Distribution board's built-in BEC that I have set to 14v.
When I run the gimbal off it's own 4S battery, I don't have this problem and the EXT_FC_Roll and Pitch monitors behave correctly.

I'm only running the Signal Wires for the signal from the FC to the Gimbal. No Ground or + wires.

Any ideas?
I'd really prefer to not have an extra battery on board just to run the gimbal.

Thanks