RL56,
My G2 unit did the same and when communicating with Humminbird, I was fortunate enough to have a G3 unit on the boat to test whether it was head unit or transducer. It did the same thing so it was recommended by factory to return for repairs. It turned out the to be the internal board in head unit which they repaired under warranty. If you know someone to test ur head unit, you’ll know pretty quick. I questioned the factory for recommending I plug in the G3 transducer, but they stated that it wouldn’t be a perfect sonar picture but it would work well enough for the test.