Hi
Thanks for your suggestions.
I’m not sure if the ESC’s are grounded.
I’ve connected in the standard way for the 3DR instructions: with all 3 wires in the ESC connected to the distribution board via the plugs on the board.
I can’t really see how this grounds them, relative to the Pixhawk (which is what I guess you mean), but I assume that they’re grounded via this distribution board in some way.
How can I check? (I have access to a cheap digital multi-meter)
I tried reducing the RC_SPEED parameter, as you suggested, but if anything it made it worse 