I am having a problem with interference on my bow mounted garmin. It has a great picture when I am not running the trolling motor but sometimes it becomes unusable when the trolling motor is on. It comes and goes. I can be trolling along and its all good and then for no apparent reason it goes south. I have moved cables, wriggled cables, flipped it the bird. Nothing helps. Does any body have any ideas? The trolling motor is a minn kota 80 lb thrust and its pretty old. Oh and the garmin is almost new.