Hey, So I recently upgraded my E5520's to X5675's. I did delid the CPU's myself without any major problems. They also got recognized by the system at the very first try and are generally working flawless. However, once the CPU's get under load, my fan speeds increase quite drastically. Running geekbench for example, boosts the CPUA and CPUB heatsink fans to around 3000RPM. When idling the speeds seem quite normal to me - maybe CPUA and CPUB are slightly to high with around 1100RPM. These are my idle stats right now: PCI - 800 (forced to 800 because of the annoying bug when starting up the mac) PS - 690 EXHAUST - 600 INTAKE - 600 BOOSTA - 1110 BOOSTB - 1110 I am using Macs Fan Control btw. These seem normal to me for being idle. BUT: For CPUA the red light between heatsink and RAM banks starts flashing randomly - only once the CPU is under load though. After reading the Mac Pro 2009 technical guide, this hints to overheating issues if you ask me. Increasing fan speeds also point towards that direction. At first, this red LED also started flashing when I booted up the Mac. However, tightening the heatsink screws sooner or later eliminated that red light when starting up. But it is still there when the CPU is somewhat stressed. And it is only happening to CPUA - CPUB is completely fine. So this led me to tighten the heatsink screws as much as possible. I am now at a point, where it's pretty much impossible to further increase the tightness on them, without applying some major force - which I am scared of because of the socket pins underneath. A list of stuff I already did: Swap CPU's around - I'm pretty confident, that both CPU's are not faulty. Check the socket for bent pins - no bent pins Do a SMC reset - already did plenty Do a PRAM reset - already did plenty Check if the heatsink connector is properly seated - already checked, but since Macs Fan Control spits out a value for the heatsink RPM, I suppose it must have a proper connection? Re-applied thermal paste - already did it 2 or 3 times Re-seated the CPU - already did it 2 or 3 times - particularly scared of this, as it's possible for the CPU to be stuck to the heatsink and all of a sudden fall down onto the socket pins bending them... I am seriously out of ideas... Don't wanna risk tightening the heatsink screws even more to guarantee a proper contact with the CPU in fear of bending the socket pins. On the other hand, CPUA needed quite some tightening to even recognize all of the RAM, so maybe I am just puss*ing to much regarding tightness. CAN I actually bend the pins under the CPU if it is delidded?!