FYI Sonar interference with MinnKota's
I know a couple people have sonar interference that use an AutoPilot trolling motor. I recently installed an AP and also getting sonar interference.
MinnKota sent me a couple wires to install. One was for connecting the negative posts from the starting battery and the trolling battery. The other was for grounding the brush plate in the motor to the ground on the control box in the head. This 'fix' did not reduce the interference.
Out of curiosity today, I turned the depth finder on while running the trolling motor. I unscrewed the hose clamp for the transducer and immediately noticed the interference had stopped. I thought I would put a thick piece of rubber between the transducer and the motor to see if that helped. It did not. While the soanr and tm was on, I re-connected the hose clamp and the interference was back. I removed the "metal" hose clamp and installed the transducer with a large zip tie. No more interference.
I believe the hose clamp was picking up the magnetic field in the motor. If you are having this issue, try the zip tie.