My new shuttle has developed a very annoying problem. The fan will make an horrendous noise on startup and continue to do so until i hit the back of the pc, this makes it stop. It sounds like it is catching on something but when I look nothing is there, I am not sure whether it is the heatsink not being flush with the back of the case. After I hit the back of the case it shuts up and is not noisy again, until another restart. Any ideas people?