RF interference can encroach into sonar units by 2 paths - xducer/xducer cable and/or Sonar power circuit ...

One should determine which of these 2 paths that the interference is encroaching ...

This is best determined by removing the xducer and its cable completely from the trolling motor and from under the deck (where a lot of power wires reside) ...

Test the xducer in the water far away from the trolling motor while keeping all of the xducer cable away from anything 12v that is not the sonar unit 12v itself ...

*If the interference is still present - it is encroaching into the Sonar unit power circuit - and no amount of xducer remedies will help ... track down where the trolling motor power and Sonar power are allowing interference encroachment ...

*If the interference goes away - it is indeed encroaching either into the xducer housing (possible rubber cable strain relief damage) or encroaching into the xducer cable (possible nick in the cable somewhere).. or xducer cable too close to trolling motor power wires ...

If the interference is indeed encroaching into the xducer or xducer cable start by testing the xducer housing close to the trolling motor housing ...

*If the interference is still present - it is encroaching into the xducer housing ...
*If the interference is not present - it is encroaching into the cable somewhere ...

Rickie