I installed a new stereo system in my boat last year and all worked fine until I bought a new head unit. The system has 4 8" speakers and a 15inch sub on a large 5 channel amp. The boat was wired completely new with all new wires and cables when the system was installed. I switched to a ken wood deck and now when I turn the ignition on or run and accessory you can hear the humm in the speakers. When I crank the motor it makes a really loud sound in the speakers while its cranking. I have ran multiple grounds back to the head unit and ground the chassis and etc. The amp is ground and powered with the large cables and mounted near the battery. A friend told me I needed a filter for the radio so I took one off an old radio and installed but it made no difference. I'm sure the problem must be obvious, but without having detailed knowledge of radio systems I'm not sure where to start. Im a bit confused that there is no issue with the previous deck and now this one has the problem, and all I did was switch decks and reconnect to the wires I just cut.
Thanks for any help