My buddy has a Macpro 1.1 (intel 2007) and his rear lower exhaust fan is going bananas. About 20sec after power on while still booting OSX, the fan revs up to full speed (~2700rpm) which is crazy for a fan its size. Its pretty ****ing loud and it stays like that. iStat Pro is reporting a northbridge temp of ~130C which is way over spec but the NB heatsink is pretty cool to the touch. We've cleared out all of the dust in the case pretty thoroughly including removing the shrouds. The next step is to clean and apply some arctic silver on both CPUs and the NB but I have no idea if that will help as the temp reading from the NB obviously wrong. We've also reset the PRAM and SMC. Oh and its running 10.5.8. We'll try a clean install of 10.6 + updates before we do the thermal compound re-application.