I noticed that my LVS34 was showing the wrong depth last time I was fishing. I was in 4 feet of water, and it was showing 7 feet of water. Sometimes it would correct itself when I moved the trolling motor but not all the time. What could be the cause of this? I've had this setup for 3 years. I didn't move or change anything, so I'm confused why this is happening now. Any suggestions?