i have a humminbird 363 combo gps and sonar with a trolling motor mounted transducer. it works fine in water over 7 ft., but when i get in water below 5 ft. or so, it does not read the depth correctly.........it keeps flashing different numbers very quickly....10, 1.8, 7.9, 8.0, .6 etc., but works ok when i get in deeper water. i have tried all adjustments to no avail..........even called the co., and they said change to saltwater mode, surface clutter adj., nothing worked. seems like it works ok sometimes on different lake............does the bottom of a lake have something to do with it, like a soft or hard bottom, grass, etc. has anyone ever had this problem? thanks!