I just received my new Mac Pro on Friday - it shipped with 10.5.4 installed. After looking at some of the new features of Leopard (had only used Tiger previously), I installed all the available updates -- these were: Mac OS X Update 10.5.5 Aluminum Keyboard Firmware Update 1.0 Java For Mac OS X 10.5 Update 2 iTunes 8.0 Digital Camera Raw Compatibility Update 2.2 QuickTime 7.5.5 Remote Desktop Client Update 3.2.2 Front Row Update All the updates were successful and no issues were apparent until Sunday afternoon. The fan on the graphics card (ATI Radeon 2600 XT) now seems to be running at full speed, regardless of what is running. Just idling at the Desktop the fan still runs at full speed. A reset of the SMC has been done and a diagnostic as been run (no problems found). Is anybody else experiencing this? If it helps anyone, I've also posted my temps below: Ambient Air 24.0C CPU A Temperature Diode 34.0C CPU B Temperature Diode 35.0C CPU C Temperature Diode 35.0C CPU D Temperature Diode 35.0C CPU A Heatsink 32.0C CPU B Heatsink 32.0C Hard Drive Bay 1 28.0C Hard Drive Bay 2 26.0C Hard Drive Bay 3 27.0C Hard Drive Bay 4 27.0C Memory Bank A Point 1 35.0C Memory Bank A Point 2 33.0C Memory Bank A Point 3 34.0C Memory Bank B Point 1 35.0C Memory Bank B Point 2 37.0C Memory Bank B Point 3 35.0C Memory Module A1 48.0C Memory Module B1 48.0C Northbridge Heat Sink 38.0C Expansion Slots 35.0C Power Supply Location 1 46.0C Power Supply Location 2 40.0C Also, I did some reading and it seems that this issue has happened to others after they appllied the 2600 XT update from Apple. The update put their firmware at version .252. This is the version that is already installed on my card. What I don't understand is that why for two days the fan never ran at full speed. It just suddenly started happening Sunday afternoon while I was burning some data to a DVD - the fan hasn't slowed down since.