Fish finder shows every paddle stroke

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I have a Lowrance Elite 4 CHIRP. I was shooting thru the hull but changed it so the transducer is in the water on a Scotty arm over the gunwale and now I see a vertical line with every paddle stroke. Anyone else have this experience and what did you do to solve it? Thanks for whatever you know.
I had a Lowrance Elite 7Ti on a Hobie once, and my buddy had a trolling motor on his canoe. Anytime he got within 20-feet of me, I would see this constant horizontal line. The closer he got, the higher up in the water column the line would be. It was just picking up the vibrations I guess, but man it makes me think of all the **** that could be giving you false fish readings.