Are you using US2? Or the bird transducer?
I was having horrible interference with the bird transducer. I was told I could add an 18g ground wire between the tm batteries and the starting battery and that would help. Or could add a ferrite ring to the birds power wire.
I chose to buy the US2 adaptor and use the front graph for Sonar and mapping only. Perfect picture now. The US2 has shielding built in to prevent the interference.