Need Electrical Help... 2015 Moomba Mondo ... High frequency noise

I am looking for some advice from people who understand/know about electrical boat issues... I have a 2015 Moomba Mondo that has a very high pitch noise coming from the dash. I have been underneath the dash and it seems to be coming from right behind the center gauges. Here is what I have done to trouble shoot the problem.

1. It only occurs when the engine is running, does not occure when I have the key in the run position with the motor off.
2. It has nothing to do with the radio, the sound is present with the radio on or off.
3. It does not increase with engine RPM's.
4. The sound is similar to an old TV used to make, that really high pitched frequency whine.
5. It isn't present at first, but increases the longer the motor is on. It starts with a morse code like pattern and then becomes steady as I run the engine.
6. I have unplugged the LCD, and one other gauge in the dash, it did not go away.

Any other ideas? Thank you for the help!

Al

A lot of old tube type TVs do make a super high frequency noise that is difficult for most people to hear. Can everyone hear it or is it just a select few?
I'm always suspect of the quality of grounds with this type noise, whether attached to the specific module or component making the noise, a dash ground junction/connector, at the helm buss, at the battery, or at the engine block.
You might try obtaining a wire tracer & probe that electricians use to identify various circuits or wires (standard item at any Home Depot or Lowes). This way you can localize the noise to a specific component. Hopefully the acoustic result that you hear has an electronic origin that will make it easier to find.

On a 2015, is the dealer not a good resource?

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Is the sound present with the blower off?
the blower makes a high pitched noise on mine that seems to come from multiple sources.

Isolate the power to all electronic devices under the dash which would be at least the stereo, any amps and the depth finder and check the boat. Any battery isolation devices?

To answer some of the questions... The dealer is over an hour away and I only have the warranty on the motor, not on the boat (bought it from another owner) so that option is out (for now). It is not the blower, I should have mentioned that I turned that off and on and it does not effect the sound. Also, I am not sure what a battery isolation device is but I will google in a few minutes. I will try the circuit tester to see what I can find that way. Looks like I will have a busy troubleshooting weekend!

Just scatter shooting here....
Is there a Medallion module in the same vicinity?
There are resonances caused by electronic components, such as aging transformers and windings, that manifest as an audible acoustic noise. But in the realm of solid state elements, I don't know?
You might read up on noise created by rectifiers.

I need to rectify this problem : )

Okay... Mystery solved but I still don't have the solution. Last night I unplugged the LCD power connector (the multi function display) and the noise immediately went away. I plugged it back in and the noise was immediate and present. So, the noise is coming from the MFD. Once I discovered that little gem of info I called Moomba and spoke with Roger. He told me they were aware that some Moomba's and Supra's are known to have that issue, seems to be some type of interference that runs into the cable (perhaps near the throttle cable) and spills into the MFD cables causing the noise. He recommended using a Choke or Ferrite on the line to see if that would reduce the noise or interference, said it has reduced or eliminated the noise in some cases. So I found a local radio shack who just happened to have them and installed them last night, unfortunately the noise got worse or the same instead of improving. This morning I am going to try to locate the throttle wire and see if the ferrite will work there instead. Any additional advice would be welcomed. Also, as I have stated before, this is not a bad MFD because the noise only occurs when the motor is running so this is not a MFD problem but more of a wiring issue. Thoughts?

To close this one out this will be my final update... Roger at Moomba said to put the Ferrites on the Purple and Black wires, it did reduce the noise enough so I can't hear it as much. On to bigger and better things!