It's a bit concerning that Seasonic PSUs might whine depending on the electrical supply however, as I'm building this PC for my brother so assuming that my electrical supply is fine and isn't the cause of this whine, I could get a replacement that doesn't whine at my house, only for my brother to report it whines when he plugs it in at his!
This is only a theory so far. I'm just trying to see if there is some explanation to a pattern we see: some people get a Seasonic PSU and have no problems, others get one and have a buzz or whine, then get replacements which also buzz or whine.
Now there may be multiple reasons for the noises but if Seasonic have not had so much success in working this out in their design then maybe it is environmental and they don't see it. I'm used to this issue from my field service experience: Customer complains of a fault, local guy goes out and field test shows problem, returns to manufacturing division, they can not find the fault because of some environmental difference and send it back to the customer without fixing it!
Some time I want to try and plug in my X series without an earth and see what happens.
Also does this whine happen at all loads? I have a very old PSU which is very noticeable at zero load if you jumpstart it with a paperclip with no components connected. When connected to a system it never makes such a noise.
Yeah, I'm just fed up with this though as I had a similar problem with my previous OCZ StealthXStream, where the fan was making a horrendous noise, sent it back to be told they couldn't hear anything, got it back and it was OK (cost me about £30 to send it there and back as well), only for the noise to start up again a few months later. So I changed the fan myself (£12) and then it apparently died completely shortly after (I assumed it was my motherboard first, so bought two replacements, as the PSU worked OK on my Gigabyte board but on my Biostar one would cut out straight after I powered up the board).
So I thought, ho hum, spent £51 on the highly-reviewed G360, which is expensive for a 360W PSU but I wanted something that was quiet and reliable to hopefully avoid the need for my brother to have to replace it for as long as possible, only to find the first time I test it that it's unusable due to this whine!
Anyway, to answer your question I've only tested the G360 connected to a motherboard with CPU (Athlon II X4 630) and 4GB RAM only. I'm not sure what load that would cause but I'm planning to test the PSU alone and jumpstart it to see if it's any different.