Good morning kokinidis1,
Thank you for your inquiry. If you are referring to the white line that is vertical on the sounder screen that occurs when turbulence goes over the face of the transducer. Based on your other post which you inquired about a P66 transducer, if you are using a P66 transom mounted transducer, cavitation, air bubbles turbulence is not uncommon.
What version of software version is your unit currently running?
C-Bass