Hi,
If any electrical gear is mounted on a metal chassis , it is worth taking a chassis earth wire connection back to a common point, e.g. battery negative.
I had a case of some earth leakage from an ESC driven motor and, without the earth wire, you could see, with an oscilloscope, the chassis voltage spiking with the ESC signal. The interference caused other servos to "twitch" badly. With the earth wire the problem went away.
Always run the wires individually to the common earth and not looped otherwise a resistance can build up and the interference may occur again.
A STRANGE EFFECT!
During the development of my flash steam boiler, the computer based controller had some very erratic behaviour, which I assumed was software related, but which only occured when steam was issuing from a test pipe. I combed through the software, wrote filtering programs for the incoming signals, all to no avail.
After some research, I found an artical about William Armstrong and his discovery of steam generated static electricity (1840s) about which he corresponded with Michael Faraday. Well I earthed down the copper steam pipe and the problem went away! Well, for all the years I spent in industry, I had never heard of that effect.
Ian.