look i am not at all sure what that is - but best guess - when you get lines of interference could be electrical interference due to power cables next to sonar cabling so maybe could try reroute the power or sonar cabling - it could possibly be air bubbles on the transducer so check if any hull defect in front of transducer or if transducer located a bit deep - other than that may need a trip to lowrance for the transducer and or the head unit for service checkiing that both working ok - others may have some better ideas
cheers