I don't think that is interference. It looks more like a bad unit. Do you get the correct display in simulation mode?
Sonar Simulator
This unit has a built-in simulator that lets you run it as if you were on
the water. All sonar features and functions are useable. When in
simulator mode, you will see [Simulator Mode] in the Sonar Page title
bar. To use the simulator:
1. From the Sonar Page, press
MENU|MENU|↓ to SONAR SIMULATOR|ENT.
2. Turn off Sonar Simulator by pressing
MENU|MENU|↓ to SONAR
SIMULATOR
|ENT|EXIT.