Interference can encroach into electronics by 3 separate paths ...Or a combination of the 3 ...:
*xducer/xducer cable
*Power wire
*Head unit (unlikely)
The 1st step in dealing with interference is to verify which path the interference is encroaching into the electronics ... There is no need in applying remedies to interference paths that are not the issue ...
Remove the xducer and it's cable from the TM (including any xducer cable under the deck that could be close to TM wires) ...
Hang the xducer in the water far away from the TM and test for interference on the display ...
*If the interference goes away then remedies for interference encroaching into xducer/xducer cable is the next step ...
*If the interference is still present then remedies for interference encroaching into electronics power circuit is the next step ...
Rickie