I've have this problem and seen this problem on tons of youtube videos as well but when I step on the trolling motor go button you can see a blurred line on the graph every time the trolling motor comes on. I don't know if its electrical noise or just the vibration of the transducer attached to the trolling motor or what. I've tried adding a minn kota noise filter inline with my batteries and it didn't work. Anyone else have this issue with their graphs and fix it? I've got a Lowrance Gen 2 Touch HDS 9 on the bow that does this. Thanks.

What transducer you using?

Which battery are you getting power from? It should NOT be one of the trolling motor batteries.

From what you say, it sounds like you have an external transducer mounted on the TM motor housing. Wondering if the interference is via the transducer or the power to the HDS? Simple test: Temporarily remove the transducer from the motor housing and mount it on something else you can stick over the side away from the trolling motor, and hit the button to turn on the trolling motor. Interference still there? You're getting it via power. Disappeared? Then it was apparently due to close proximity to the trolling motor.

Do you have a minn kota motor? (Guessing you do as you added a MK filter.) Does it have a transducer built into the trolling motor? If so, there's a fuse inside the head of the TM that may be blown. Electronic noise can be more of an issue if that fuse is blown.