Greetings! I've been reading the last couple of days about PSUs since I got burned by a Seasonic SS-660XP 2. It had an annoying coil whine and the replacement as well.
Welcome to SPCR.
Have you seen this:
Last week, some six weeks after this review was originally posted, I received a third sample of the Seasonic 520W Platinum. This one is apparently representative of the current production models. I tested the new sample 3 times, with many hours of steady modest load (<100W) and also standby between high load testing, over a period of 5 days. All this was to ensure that no changes occurred as the unit "broke in". http://www.silentpcreview.com/article1313-page5.html
Overall, the level of whining noise of the third sample is very low and did not change over time or load. It is very unlikely to cause any negative reaction with 99% of potential users. (The 1% who might complain are the ones who would never be happy with any product.) I would call it a residual level of noise — not audible when one's head is more than a foot away, under any load or acoustic background. There is a wee bit of whine associated with the 5Vsb line, and it varies a tiny bit as that load is raised and lowered, but not to any significant or noticeable degree. As a function of 12V load, the level of whine is very low, and does not vary. When the measurement microphone is placed right atop the PSU, the frequency of the trace noise can be seen as spikes at 4kHz and 6 kHz, but even from this intimate distance, the levels are just -10 dBA and -15 dBA.
The very low level of electronic noise achieved in this sample is nice to see. Seasonic reps assure me that the issues which caused the higher than expected electronic noise in the original sample have been resolved. Apparently, it is the quality of the winding process for the transformer that affects the noise I found, and this issue has been identified and corrected, with continuous monitoring assured for the future. Typical production variance of the electronic noise from my sample is estimated to be approximately +7%, -5% — this is very tight tolerance, and a +7% increase will not be audible as any change at all.
The electronic noise with the second sample really wasn't serious, and this one is much better, so all in all, it's a very positive result.
As mentioned in the review, Seasonic reports that adjustments in the BIOS of some recent motherboards eliminates electronic noise completely with many earlier production samples. The settings are:
BIOS set up to ENABLE ErP/EuP (S4~S5)
BIOS set up to DISABLE Audio Always On
There seem to be 2 camps on Seasonic PSUs: those who suffer from the whining and those who don't. I've never had it with my X400 even under test conditions with everything else off. Seasonic seem to have found some issue with some Platinum models but there remain these BIOS options to try too.