I have a similar but worse problem right now. When I push the button for my jack plate it knocks out both bottom machines and my electric shifters. The shifter part is a PITA as it automatically throws the boat into nuetral no matter how fast you happen to be running at the time. My guy says it sounds like a grounding issue.
My whole boat is kinda whacked actually. Having the entire thing stripped down to zero and rewiring everything. Every hose, switch, panel, bus bar, wire and connector. Ten years has taken its toll.