I have a 431s and initially I thought it was giving me a false shallow water alarm and then I figured out it was giving me the alarm in the same place each time. There is supposed to be a 20 foot depth where the alarm was going off. If I avoid this area then I rarely get a false alarm. The only thing I can figure is that my lake has lots of buried timber from when they flooded the lake 50 years ago and some of it is still sticking up far enough that the Garmin flips out that it sees something "big enough" and changing depth fast enough to trigger the alarm. Make sure you aren't always getting the alarms at the exact same locations before you consider them to be true false alarms.
Thanks for the response. I checked the bracket (while swimming) and it is tight. I have the transducer set at horizontal. Maybe a should try setting it at a slight angle.
I wish it only went off in one place. Unfortunately it happens often at various locations. The bottom of Lake Winnipesaukee is very rocky and maybe that has something to do with it although it shouldn't.
Well my next guess would be either 1) bad transducer connection or 2) too much turbulence around the transducer...