What part runs when key is on Acc and Ignition switch is on?

[Chexi]

Mine has only 1 ballast pump (hard tanks with 1 pump and separate seacocks), but it could very well be the culprit. I will check on Saturday when I get down to where my boat is in dry storage and report back.

[Chexi]

Mystery solved. It was indeed the factory ballast pump. I will have to remember to shut that thing off.

Even though I found the issue, I also re-wired my head unit red line (key-hot) and tied it into my yellow always on. This completely separated the systems and had the added huge bonus of cutting down about 95% of the noise I was picking up. Now you have to have absolute quiet and put your ears up to the speakers to hear any noise at all, and even then it is very faint. Before you could hear it from any seat in the boat if the volume was turned all the way down.