Joe Public wrote:
If it's intermittent and duration is random, it might be due to variations in AC quality on the electrical grid?
This is a real, documented issue for lots of electronic power equipment. Not just Seasonic PSUs, and not just computer PSUs. AC power in many places in the world are subject to a host of variations:
- voltage (up/down by 10% or even more)
- frequency (up/down, not stable)
- distortion in the waveform: This could be the most common culprit. It can be caused not only by the electrical utility but also by feedback/noise introduced back into the AC line by poorly designed gear drawing from the same power box (like in a condo or apartment building).
Over the years, I have had discussions with SPCR writers and forum members in NYC, LA, and other parts of the US about issues with AC power quality & consistency. I am sure it happens elsewhere in the world.
I suggest you monitor the time of day that the buzzing occurs, over several days or even a week. The fact that many of you are reporting the noise even when the PC is powered down suggests an AC line issue. It's not clear whether the Seasonic X models are particularly susceptible in this regard or whether they allow the PC to run quietly enough without the masking effect of a fan that the buzzing is more clearly audible.
Those who have access to an oscilloscope or any kind of AC power analyzer should try monitoring the AC waveform when the noise is occurring badly. (Naturally, you better be careful and know what you are doing, as AC power can kill you.) Finally, it might be worthwhile to try different types of line conditioners or filters to see if they can reduce the buzzing.
For what it's worth, the very first pre-production X400 sample I received suffers from a bit of buzzing, but it's low enough that when mounted in a PC with any fans in it, the noise is rarely audible. All the other X series samples buzz too little to be consider audible... and there is a good half dozen X series PSUs at work in the lab.
Keep in mind that Vancouver has excellent AC quality, and the electric service box in this house is generally very good. I have heard the effects of AC waveform distortion in some gear here from time to time, though -- audio amps with large transformers in them sometimes get buzzier at peak demand times -- evenings. I can't recall any PC power gear with such buzzing variance, though.