There can be several sources for noise in your system. First, in general, there is always noise - in any audio system... In absence of signal, there is noise. What you want to do is optimize the Signal while minimizing the Noise. In other words, most any system, even a well tuned system, can have noise, the thing is that the Signal needs to be far above that. Signal-to-Noise is always expressed as a ratio. The Noise is given a value of 1, then the Signal is calculated as a ratio above that. But there is always some noise at the bottom... Referred to as the "floor", as in noise floor.

First, thing to check is the AD Input should be set for LINE input if nothing is plugged in. The MIC/LINE a parameter is controlling an amplifier. If the AD Input is not in use, the AD Input switch should be Off. If nothing is attached (referred to as the "load") then you should minimize the gain from that amp.

Other sources of Noise: when connecting your keyboard to any other device, your system is subject to ground noise. A ground issue can be easy or difficult to track down and is caused by interconnecting electrical devices. It will manifest itself in your system and wind up coming through your speakers. Electrical causes for ground noise can vary greatly and there is no one solution that works globally.

Plugging all devices into the same source, often cures problems where two different electrical lines are the cause.

The nature of the sound of the ground noise is one clue... For example, here in the USA you might run into 60 cycle hum, which is a low frequency buzz often heard when polarity is a problem. The power supplies in many electrical devices here run at 60Hz. With computers a ground noise can sound like a high pitched zinging noise when connected by USB, that pitch changes up/down with hard drive activity (so it is particularly annoying when attempting to record/write audio to your hard drive). Ensure that your computer is grounded as recommended. You may completely clear up computer ground issues by running your laptop on batteries (if the noise completely disappears when you run your laptop on batteries, you have identified a source). Obviously, running on batteries probably should be avoided, but this can help you track down what type of issue you have and should lead you to a solution.

Solving issues of ground, once the cause is diagnosed is usually easy. But in rare cases it is a major problem with electrical sources in your area of the country or part of the world. Consult local electrical folks or your local music store for solutions. I've learned that providing blanket answers (even when well intended) does not always get the job done. Without a complete description of what you have connected, where in the world you are located, and the nature of your cables and connections... It is all just well intended guesses.

No one wants to tell you something that causes you, or your gear any harm. Yes, some times it is a very easy fix. Other times, not so much.
If you are in doubt about how to solve the ground issue, please can your regional Yamaha Customer Support office, they will either be able to help you or direct you to where to find a solution. Let us know.

Thank you for your pro and detailed explanation, for your patience too 😉
anyway,first I've set the A/D input ---> Mic/Line to Line . Then, I've tried to run my laptop only with batteries, but the slight hum noise is still there.
I'm agree with the fact that it is a ground loop noise type, maybe my home lacks of a grounding system and the active speaker "highlight" it.
Along with the MOXF6, on my laptop I keep connected the soundcard ( Steinberg UR28M), the Steinberg USB eLicenser for Cubase 8 and other two generic usb pen drives, who knows if the sum of those on only one laptop could be the issue.
I will give a try by moving myself with MOXF and Laptop in another house to see if something will change.

Now I have another question:

In Voice Mode, I select a Voice from Category Search, in my case I choose "PRE1 D14 DX5-Zero" under Keyboard/ FM Piano folder,
well, I've noticed that when I'm in Voice mode, the DX5-Zero preset has 5 different kind of arpeggiators,
but If switch to Song/Pattern Modes, then I choose the same sound (DX5-Zero) from Category Search it now has only 1 Arpeggiator and not more 5 kinds, even when I enter in Rec mode, why?

A common mistake is to turn the active speakers up beyond what they are designed to do. Here's how that can easily happen. Most musicians are very much like guitar players - they treat all knobs as VOLUME controls, particularly when they actually do affect the OUTPUT level of the overall signal. They just turn the knob UP until it is loud enough.

Often on active speakers, Studio Monitors in particular, you will find that they take the time to identify the control on the back panel as an INPUT SENSITIVITY CONTROL. This is technically correct. You are to match the level of the incoming signal. So your MOXF is rated at either 0dB or +6dB as its OUTPUT. You should set your Input Sensitivity accordingly. You will notice on many monitors the more you turn UP the knob the lower the value on the knobs scale - a clear indication you are matching input sensitivity. The weaker signals need more from the amplifier than stronger signals (make sense?)

Simply turning up Active Monitors toward maximum will reveal NOISE at some point. As I mentioned there is always a "noise floor". It's there. You will find when you set the OUTPUT LEVEL knob (Input Sensitivity) on your Monitors properly, that much of the residual noise is inaudible... which technically is called "negligible". You want to set your Input Sensitivity properly - this will eliminate your Active Monitors from being the source of the noise.

If, for example, you turn your monitor's amp up so that it is matching a -10dB source (like a consumer tape deck) you might find you are hearing excess contribution from that "noise floor" - try lowering the INPUT SENSITIVITY to +4dB (usually at about 12 o'clock on the knob).

This can eliminate much of the noise from the speaker's amplifier. It is no reflection on the amplifier - that is what they do - they output SIGNAL and that always includes NOISE. It is the operator's task to optimize this. There are no noisy amplifiers, only noisy use of the amplifier... in other words, noise is part and parcel of the system. We simply always opt to work where we maximize signal and minimize potential for noise.

So yes, there is a limit to how loud you can get with your studio monitors. Set properly around +4dB is a good rule of thumb. At that setting you should not be able to hear much noise contribution from your speakers own amp, not with the MOXF connected.

If you find that your speakers are not loud enough, you may have more headroom in your mix than you considered. The MOXF is rated at either 0dB or +6dB on the output (found in UTILITY mode), but that is when all channels are output together. Mostly you are probably not even close to outputting +6dB in normal use. Plus most MOXF Voices are very conservatively set as to volume.

But I suggest checking your monitors - make sure they are just not sitting WIDE OPEN... the noise you get from that, is actually listed under 'user error'. It is similar to having the AD INPUT set to MIC and the pre-amp up full... you will hear that, for sure, especially when nothing is connected. If a mic was connected you'd immediately turn that down! Unnecessary GAIN from the amp - set the amp lower and send more signal in!!! Gain Staging.

In Voice Mode, I select a Voice from Category Search, in my case I choose "PRE1 D14 DX5-Zero" under Keyboard/ FM Piano folder,
well, I've noticed that when I'm in Voice mode, the DX5-Zero preset has 5 different kind of arpeggiators,
but If switch to Song/Pattern Modes, then I choose the same sound (DX5-Zero) from Category Search it now has only 1 Arpeggiator and not more 5 kinds, even when I enter in Rec mode, why?

Because arpeggios are musical phrases. They are independent from the VOICE.
If the DX5-Zero is an electric piano emulation - it is the instrument, then the 5 Arpeggio Phrases you see associated with it in VOICE mode, are just something that this instrument is capable of playing. They are NOT apart of the VOICE. They are 'extra' stuff added to the VOICE.

When you move the VOICE to a SONG or PATTERN, it is like a musician taking that electric piano to the studio.
The Arpeggios (the phrases that were associated back in VOICE mode are not automatically copied)... the VOICE can use any of the more than 7900 arpeggios in the MOXF... They do not AUTOMATICALLY come along.

Yamaha does not presume you have to use them, that you even want to use them... they are suggestions.

If you would like to COPY the 5 ARPEGGIOS that were suggested, by Yamaha, in VOICE mode to YOUR SONG or PATTERN, you must do the following:

Go to SONG or PATTERN mode:
Press [MIXING]
Press [EDIT]
Touch the PART number 1-16 that you want to place this VOICE "DX5-Zero"
Press [F1] VOICE
Press [SF1] VOICE
Set the parameter "P.with Voice" (Parameter with Voice) = ON
Move the cursor UP and select the VOICE

By turning PARAMETER WITH VOICE to ON, now when you select the VOICE for this PART it will also COPY the arpeggio phrases that were associated back in VOICE mode. You can use them, or you can change them to others. Remember any VOICE can use any ARPEGGIO (some make more sense than others but the point is ARPEGGIOS are totally separate from the VOICE) Hope that helps.

The TEMPO is also not copied... because Yamaha does not presume to know what Tempo you want to play them...

🙁

You can blame any component you like, if it makes you feel better. Noise is probably still there, you are just hearing it less well. Ground noise is usually removed by fixing the ground situation. Hopefully, you at least now know it wasn't the Keyboard! Ground noise is caused by the interconnection of products, blaming one item (makes you feel better) but does not really answer the cause. A USB cable with a ground shield can indeed be a solution in situations where a ground issue arises. But sometimes it is not that easy. Glad your issue is fixed.

(Nobody ever blames the speakers, they're reproducing the hum.... funny, you turn them off the hum goes away... but they will blame everything else. It's obviously silly to blame the speakers... my point is, it is just as silly to blame any single component, it's always a combination of items. Lifting the ground properly is the way to go.

🙁

🙁

I was also having this problem. When the USB from my Yamaha Motif XS was connected to my MacBook I would hear a variable whine, but not when the MacBook power was unplugged. After reading up about ground loops on Wikipedia, I did some searching and found an article which matched my symptoms. The fix was the same too: a $35 USB isolator: https://www.keyboardwaves.com/remove...-audio-output/

Gear: Focusrite Saffire 24 DSP, Macbook pro, Cubase 10.5, Yamaha Motif XS