fyi, I seem to have solved my HB561 interference issue caused by Terrova / US2 (transducer inside) TM so I thought I would share the good news. Like everyone says, contact Humminbird service for help first. Do this before crazy things like grounding your trolling motor etc. Mine was fixed by: turning on Noise Filter to High3 in Advancved menu AND switching to 83hz transducer signal setting. Even with noise filter on hi I got interference on both 200hz and 200/83hz dual setting. HB support still sent me a ferrite choke for free which I may install in case I want to use the 200hz setting in the future. Oh yeah, be sure to have unit powered by cranking battery too and not the TM batteries. I attached pic of the interference in case this is what you see too.
Hope this helps!
![Grin ;D](http://forums.sideimagingsoft.com/Smileys/classic/grin.gif)