The fan is intermittently noisy with a fluttering sound and/or running fast. I have blown out the vents with compressed air but that doesn't appear to help any more. Blowing air from the outside to the inside seems like it would just move dust from where it is to where it can insulate other parts. It appears to me that the entire bottom has to be removed and I can not find instructions for that. After removing the small phillips head screws do I use a knife or screwdriver to pry the bottom off and how much force can be used when it sticks? Are there any Gotchas waiting to break anything?