Can you remove the xducer from its mount and hang it in the water farther away from the TM ...??

This may tell us if the RF is getting in thru the xducer or in some of the other wiring of the unit...

RF can infiltrate into the unit by a few possible paths...:

*Xducer cable
*Power cable
*Head unit itself
*Ethernet cable

We have to determine which path your RF is getting into the unit before we know which cable to put the ferrite core on...

Rickie