This is definitely Sonar Crosstalk. The Mega Live Interference Rejection feature only works with Humminbird sonar sources... It manages the pinging sequence and duration of all network connected sonar sources. Since it appears that you have Garmin, the Interference Rejection setting is doing you no good. I know nothing about Garmin settings, but if you have control of things like CHIRP ranges on your SI or DI, you might want to play with different frequencies.
