Sonar/trollimg motor interference

I’ve got a problem that just started on my last two trips out. When I put down my trolling motor, it messes up my sonar screen. The normal white with orange images turn to blues and blacks. It’s almost like a negative. I can still see some of the images but it’s all dark. As soon as I pull the trolling motor up, it goes back to normal. The first time it happened, I thought that it was a low battery problem. I was only reading about 9 volts. But yesterday, my batteries showed a good charge at 12.5 volts. I usually charge them the day before I go out. I have two deep cycle batteries hooked in parallel, and the only things I run are my trolling motor, live well, and my GPS/sonar. Yesterday, I didn’t have the live well. Oh, and the GPS is never affected.
I’ve had this boat(16’ alum. jon boat, 40hp Evinrude) for 4 years with the same set up, with no problems.
Any ideas?
Thanks, Bob

Bob Van Gundy
Marine Designs,Inc.
Custom Aluminum Fabrication
803-727-4069

Bad ground on your sonar unit? Try isolating the trolling motor on its own battery and not hooking the two in parallel. Probably just need to clean connections.

'06 Mckee Craft
184 Marathon
DF140 Suzuki

That’s what I was thinking, but wanted to get a second opinion. Thanks.

Bob Van Gundy
Marine Designs,Inc.
Custom Aluminum Fabrication
803-727-4069