Lots of info here about dealing with interference ...
http://www.crappie.com/crappie/fishi...-interference/
TM interference is usually caused by the PWM Pulse Width Modulation feature TM'S use to save battery power ... It can be challenging sometimes to track it down and deal with it ...
What works on some boats may not work on others ... And some require more than one remedy option ...
The most common scenarios are separating TM power wires as much as possible from the xducer cable and using a battery for the electronics separate from the TM battery(s) ...
Rickie