My Alpha PAL6035 with a YS Tech 60mm fan was making a lot of noise and creating some equally noisy vibrations in my Lian Li case a few weeks back. I took a look at the fan and it had a good amount of dust that had accumulated on the blades. This caused the fan blades to become unbalanced causing the vibrations and that extra noise. I added a wire mesh filter to the front of the case that quickly stopped that from happening again.
It can gum up your CD, cause instability problems, add unwanted heat to your system, etc. It's always a good idea to periodically pop your case open and duff up your components, and where you can, add fan filters to try to keep dust to a minimum.
Better than Wire Mesh Filters to me is the Foam Filters used on Home AC Units. I did this on two Ducts that were cut into mine and my wifes PC's. Works wonders! She smokes and i kept having to clean out her PC all the time......i smoke Cigars every now and again so i used to clean mine too. I have had the filters in for Two months now and both cases are MUCH cleaner than they used to be. Nice Cheap Solution....my favorites!
i found that the best way to control the amount of dust inside your case it to put home furnace filters over the inlets into your case, also i usually give my case a good vacuming about every week or so, actually, i am going to do that right now...