Beast Master - Deep Rock Galactic Wiki (fandom.com)
I play with the googly eyes mod, and he lives on my mic boom.
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A good simplified way to explain the noise issues is how PWM fans work, or a modified sine wave vs simulated
The power is pulsed, and those pulses are timed. Having too much amps arrive early or late results in the voltages rippling up or down, as the phases turn on/off to adjust for the changes in power demand.
remember that they're pulsing it to match changes in demand.
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Depending on where in the setup you're at, power could be coming in or out as either side of this image - being converted from one the other.
multiple phases are used so the square setups compensate for each other, so the steps are smaller - but they can go out of phase (hah) with each other too, if the incoming voltages are different between them.
You'll notice it's the current that varies here, not the voltage.
They use multiple phases and try to time them to provide as smooth a curve as possible, but when power consumption (current/amps) goes above or below the happy range for the components or voltages are higher or lower than expected - you get noise like a squeaking door as they're forcing themselves to shut against a strong flowing current
Actually, closing a door and having air whistling past is also a great example of how to explain this.
Low voltage with a higher current, the door/gates have trouble opening, while high voltage and low current you get sqeal as some of the current sneaks past after its meant to be closed.
The timings being off results in the square looking output, and voltage ripples. Capacitors can smooth it out again, but only so much.
On the CPU and mobo side, definitely look into altering how the system idles - even something as simple as the high performance power plan in windows could have an effect there, as it definitely did back on the x58-UD3 gigabyte boards back in the day where low idle wattages resulted in single core CPU usage being audible over the onboard audio as you moved a USB mouse around.
For GPU's we're a bit more limited, as we can only try changing cabling to reduce resistance (smoother/higher voltage inputs), or altering clock speeds and voltages up or down to get them out of whatever unhappy state they're in, without physical modifications