Originally Posted by Btye1
Did you ever really resolve this high pitched noise. I am doing a stereo in a guys 2012 x45 and am having the same issue. Have already put the head unit and wet sounds eq on the same power and ground as the amplifiers and put a relay in to bypass the ignition switch. Looking for some help here. Next step is going to be a ground loop isolator but wanted to check here first since this seems to be a mastercraft specific problem.
Did you feed the head unit's memory/main power from the cables as the amplifiers, or just isolate the switched wire? EVERYTHING to the head unit needs to come from the amplifier feed, including the ground. Loop the head unit's ground to the screw on the back (this should have a support strap on it, too) and connect a new ground wire to it. Run that new ground to the distribution block for the amplifiers' ground. DO NOT connect the ground wire from the dash- cut the terminal off and secure it to the harness, but don't use it unless you want to add some kind of accessory. The switched red wire in the dash- If that's latching a relay behind the head unit and you ran a new wire from the amplifiers, connect the head unit's yellow wire to the feed wire, ahead of the relay.
Using a ground loop isolator may screw up the sound- they're not all made well and sometimes, it sounds bad (decreases bass response). Seems unlikely, but I have heard it happen.
Are the audio cables bundled with wires that carry 12VDC? If so, move them away. If you want to find out if the noise is being induced, unplug the cables from the head unit's output jacks- if the noise continues but disappears when you touch the plugs (or short the tip to the ring), it may be induced. If the noise stops as soon as you unplug the cables from the amp, it's probably a ground loop.
What gauge is the power and ground cable going to the amplifier(s)? Isolate the audio system from all other circuits, meeting them only at the battery posts. Measure the voltage across the battery terminals and then repeat this at the amplifiers' + and - terminals with the system turned off. You should see no difference in voltage. If you do, find out why.