I just purchased an 850w yesterday after my Zippy PSL6701 (modded with a quiet fan) blew up at a Lan due to dodgy power grounding that killed a few other pc's
Anyway, the 850w has gone into a system with interesting specs, it has 14x Samsung 750gb hdd's, 2x seagate 80gb 7200.9, 1x Seagate 7200.12, 1x optical drive, an E8400 cpu, 4gb ram, a Gigabyte P45 motherboard, 2x Intel SAS raid cards, an 8600GT graphics card and about 10 fans. No it isn't quiet but I do go to SPCR regularly because I enjoy the power supply reviews.
The one thing that concerned me is that while I'm loading up the 12v1,2,5 and 6 rails I don't actually know what transformers they are pulling from. There are two big transformers in the unit. In effect it has two rails that are split into 3 lines with OCP on each of those three lines.
What I'm guessing is that the pair of pcie connectors built in and the pair of pcie connectors are on different transformers. IE the two built in have one on 3 and one on 4. This in turn is coming from the two transformers. In turn the two modular pcie connectors on 5 and 6 are also going to be on one transformer each, so the sata and molex connectors are on different transformers, and in turn I'd suspect that 12v1 and 12v2 are on different transformers as well.
So my final guess is that 12v1,3,5 are on one transformer and 12v2,4,6 are on the other. It would be great if someone at Zalman could confirm this but I doubt I'll get a reply.
Peter - perhaps yours in faulty, mine doesn't make that noise at all and I'm sure if it was a common problem other people would make mention of it too