[McGillicuddy]

My first thought would be power/voltage or electromagnetic interruption from other wires, then settings.

You've probably considered this but a couple of thoughts... Resetting the sounder unit to factory defaults. I don't know the unit, but check the manual to see if this is possible. If you don't have a manual scout around on-line. I've run across several in the past.

But first, check the the transducer cable connections, and cable route. Make sure it is not crossing over or running adjacent to any wires or cables going to the motor or starter. Info is easily scrambled by nearby power or electromagnetic sources.

Voltage fluctuations are also very detrimental to transducers ability to relay the depth info to the unit. Make sure the battery it runs off is fully charged and wire connections aren't creating unwanted resistance. Imagine trying to do something on a computer and your power strip is kicking on and off; or that the cable to your modem is just loose enough that you sometimes can't connect to your server or CSC until you jiggle the cable... See what happens when you put a magnet next to your tv or computer monitor... Good luck