I could imagine an OC'd i7-950 and OC'd 2x GTX480 pulling very close to 850W, if not slightly more (~50+W). A quick search of 2x GTX 480 isolated
power consumption comes up at 600-650W
(link is of stock clocked engineering samples... driver and firmware updates create some variance). The i7-950 has a TDP of 130W (some link
, power consumption was not isolated from mobo or idle GPU). We can say that your motherboard and everything else draws 60W conservatively. Already, that is ~800-850W without overclocks
. Now imagine what happens to power consumption when those components run at speeds above their rated spec with volt mods
. I'm not by any means an electrical expert, but I could imagine your sound issue and eventual crash being caused by electrical noise (increasing over time?) from your PSU, OR just a simple build-up of heat in the PSU inducing poorer performance and creating more noise/ripple. Alternatively, the degrading sound issue could be caused by an accumulated electrical charge somewhere that is discharged when you reboot your PC. Those are my first hypotheses at my current level of understanding.
Some anecdotal support... As I was sifting through the PSU section a while ago, I recall Phaedrus, our resident PSU guru, mentioning the GTX 480's "poor scaling" with regard to power consumption when overclocking, possibly SLI as well. Also, I came across
this excerpt which you will find very relevant:
Originally Posted by GTX 470 - GTX 480 - GTX 480 SLI Review at HardOCP
With a nicely overclocked Core i7 920 processor (3.6GHz) and GTX 480 SLI, we saw at the wall wattages exceed 900 watts at the wall in some very stressful GPU system situation.
Since they measured the power draw at the wall, however, then your HX-850 might only be working with 756W (900*.84 @100%), and it should be capable of 1016W vAC
"at the wall." So there's that to consider too.
I would first see turn off your GPU OC's completely, then remove your CPU OC/reset BIOS, then revert back to single GPU configuration.