Bought a used 5,1 and just did an upgrade from dual 2.4ghz quad to dual 2.4ghz six-core (x5690) CPUs. Post upgrade, the new chips seem to be running as hot as everyone elses (40ºC-84ºC), so nothing out of the ordinary there. With the stock ATI 5770 (1 power cable) that it came with, everything is quiet as can be, but as soon as I put in my MVC Nvidia GTX 570 (2 power cables), the machine gets a little louder. I notice the Expansion Slots fan and the Power Supply fan ramp up in speed. The Expansion Slots fan speed went up to around 1600rpm and the Power Supply fan went up to 1100rpm and stayed there for about half an hour. For whatever reason, the speeds came down on their own. The Power Supply fan is now sitting comfortably at 600rpm, and while the Expansion Slots fan speed came down, it's still running at around 1000rpm without any load on the machine (machine booted up to Finder, no apps or benchmarks running). Comparatively the Expansion Slots Fan with the ATI 5770 was just 800rpm. Is this normal? I know 1000rpm isn't much more than 800rpm, but it's just enough for me to hear them, especially when I do something a little graphically taxing and there's more GPU demand. This card and my 3,1 Mac Pro were always whisper quiet, so I'm not sure what's going on differently with the same card in the 5,1 to make the Expansion Slot fan run a little harder. Anyone have any ideas?