Electrics/electronics is a definite dark art, being mechanical all my life and now only getting into electrics I have found this out.
Working with electricians who have been at it for all their lives they too find hard with ground loops, feedback, earth impedances, shielding and so on, especially with modern day control equipment. It has become a very scientific art to make every component work together without interference of some form or fashion. Following the manufacturers guidelines is a must, but for some people decide they know better and go their own way. Good test equipment again is a must but unfortunately this is financially beyond some. So it boils down to advise from guys who have been there and done it, for that I take my hat off to you and thank you for the time, patience and effort you put in to helping us lesser mortals through the dark art of electrics and electronics. Definitely without Tweakies help I would not have Scrappy up and running.
Stewart