Carldon,
Welcome to the forum. This looks like interference from your engine or other electronics. What unit do you have? Have you changed anything else? Like wiring or added other electronics? Are you running any other depth finders or were you near any other boats with depth finders when this was happening?
Also, tell us in detail about your setup. Units, Interlink, number of transducers, switches or y-cables, weathersense, trolling motor, etc.
The more we know the better we can help!
Good Luck,
Robert