Erm...After checking the parker sd3 specs it says bipolar drive so MC could be right and it's shielding or something. . . . More investigating needed me thinks.

Think best thing you could do scnc is take john up on his offer and throw it in car and let him check it out.! If it's been working then chances are it will be a quick fix or just a setup issue.
At the very least he'll be able to check out what stuff is and where it goes.!