I have a 3870 X2 that the C-clip came loose and caused the fan to drop just enough to cause a chattering sound. I was able to fix this very easily as I have much experience in Technical repair in Avionics, which is what I do now for a living. If anyone else needs this type of repair then you can do it yourself. Just use ESD (electrostatic discharge) safety practices and make sure you have some thermal compound on hand to replace the old locations with. The other nice thing is you can deep clean the heat sinks and all the other dust. Be sure to handle the card on it's ends so you do not apply any force on the components. SMT (surface mount technology) components are small and easily damaged when pressure is exerted on them. Once you get down to the three remaining screws that hold the fan in place there is a sticker that once removed allows access to a small black rubber gasket. Hold it straight up so nothing falls out. Once this gasket is popped out you will see a small plastic C-Clamp laying inside. Be very careful not to pull the fan from the magnetic field or you could lose the power of the fan speed. The magnetic field is what allows the current transfer between the coils and the magnet which drives the fan. Use a light touch when pressing the plastic clamp back on as it can be broken easily. You will know when the clamp is in place as the fan will not have so much slop when you spin it by hand. This entire process should take about 30 minutes. I hope this helps some of you out there.
I know, I should have taken pictures but I did not think about it until after I finished. Sorry.