tl;dr Unfortunatly still no solution.
A technician just came by with a 105K-34810 power-supply (Which was suggested as a solution by previous message).
Still makes a horrible coil-whine noise when in Sleep mode.
It's using a TDK 2430-X14, Suppsedly from 04-2014.
I have the same problem, and if I could I would sell the printer right away. Defenitively not to recommend.
Is there a solution?
Sorry, This is really NOT meant to be a snide comment. But, I suspect you have young persons hearing. Can you test and say if the sound would bother an old person say 50+ years?
I am intersted in how hearing changes with age. I am 62 and consider myself to have good hearing. Mine is audible but not bothersome to me. My wife can't hear it. The grandchildren can.
How old are you?
I suspect some acoustic wadding (a bit of old cotton towel) strategically placed, being careful about heat disippation and flammability etc would help.
Or if you can locate the offending torroid, there may be a way of specifcally acoutically dampening that.
I suspect there may be considerable variation between idividual printers too.
I had this problem a year ago, contacted xerox and they switched out the power board for one without coil whine. That's the way to do it. If the noise is still a problem then return the printer and buy something else.
If you're stuck with the printer then there's not much you can do about it. I narrowed down the coikl whine on mine to one component, which appeared to be an un-potted custom coil. So if you're feeling adventurous you could replace the bothersome coil with a high quality potted alternative that has the correct specification. Alternatively take out the coil, disassemble it and reassemble it whilst smothering it in epoxy. That will stop the vibrations and hence the coil whine.
Call your local Xerox authorised service. An engeneer ordered the new power supply and within a week came and changed it on my printer with no charge. No issues any more.