RFI is random in occurance and there's no one sure fix or combination of fixes ...
It would save a few chased rabbits to 1st determine if the interference is encroaching into the xducer/xducer cable or encroaching into the Sonar unit power circuit ...
This is easiest to determine by completely removing the xducer (and it's cable) from the trolling motor and test it in the water far away from the TM ...
*If the interference goes away the RFI is encroaching into xducer/xducer cable ...
*If the interference is still present the RFI is encroaching into the Sonar unit power circuit ...
This is important because it's really unnecessary to apply remedies for RFI encroachment into the xducer/xducer cable if the RFI is encroaching into the power circuit ... (and vice versa) ...
Here is more info ...https://www.crappie.com/crappie/fish...-interference/
Rickie