Audio Engine Hum in Speakers

[arotoli]

I have a 2014 Moomba Mondo and when I reconnected my Speakers\Stereo\Amp to the Battery this season, I am getting an Engine Hum when I start the boat in the speakers.

What should the wiring be to avoid this? I do not have a separate battery for the speakers\stereo\amp. I have two wires (red and black) coming from the Amp. Should the black\ground be grounded to metal on the boat not the battery itself?

Thanks