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.
RIP little Nitro