Odd problem with Eagle sonar on Minnkota US2 transducer, help please?

I have an Eagle Fish Mark 320 up front connected to my Minnkota I-Pilot in order to know exactly when the front of the boat is over the tree I wish to fish. I also have a 797 SI on the boat with its transducer on the stern.

Yesterday I switched the Eagle off of fish ID because of the slow speed we were working with would not show arches so no fish were being ID'd on it. When I did that the entire screen went almost black as if the sensitivity was fully up, which it was not. The I-Pilot was turning at 1/2 and I kicked the speed up to 1 and the screen noise went away as soon as the button on the remote was pressed. Go back to 1/2 and the screen was full again. Then I found that with each 1/2 increment on the trolling motor the screen on the finder would alternate between filled and working correctly all the way up to full speed.

Anyone have an idea why or how to fix it?

Sounds like and EMI harmonic. Install a ferrite choke.