The speaker level imputs are going straight into the amp, no adapters (though the guy at Best Buy suggested to always use them).
I am, however, wondering about the ground to my head unit as I was "screwing around with" a lot of the wiring under there, near the end of the "project" and, therefore was getting pretty impatient and tugging on a lot of stuff. I may have loosened the connection -- and I like the idea of a central ground, though to get from my head unit to my amp requires going all the way around the back of the boat which makes for a lot of cable routing! (which sucks!!!).
I found a pretty good diagram on the Crutchfield website that gives ways to try and isolate the problem (
http://www.crutchfieldadvisor.com/S-hi3wV4rXzpF/learningcenter/car/amplifiers_noise.html ) that I'm going to try and see if I can figure out where the noise is being introduced before I undertake a lot of "redos"!
Thanks for all of the help and input guys -- I appreciate it. There's nothing worse than listening to your new system with the boat on the trailer and saying "damn, this sounds pretty good" and then cranking the engine and hearing ... "whinnnnneeeeee" the whole time!