how did you get the filter out of its box to clean it???
Stefan, have in mind that taking the filter out of the cartridge is not a supposed to be doe by the user (at least is not in the camera manual), which means that I don't know until which point it can disable warranty in case of bad use, so do it ONLY at your own risk. That said i've done it a hundred times without a single problem, I usually clean only the front part of the IR but sometimes some particle goes back. You know how brushes are, sometimes you end up putting more dust than there was, I usually put the filter near or against a light to see perfectly all kind of dust.
That said the steps are simple, I post a photo as a reference:
1: Move the knob to the move position
2: Hold the two small metal pieces on top while pushing the plastic knob to take the filter out. Don't push too far away, just enough to clean it without taking it all out of the cartridge. The filter itself musn't be touched. You should 1st do some tests in how far u can take it out of the cartidge before u start with its cleaning.
3: Clean and push down again, it's possible that you'll have to push the metal parts again to close the cartridge.
You won't see the filter in my photos becasue my camera is on service because of bad firewire connection.
My camera was also more dirty the day I recieved it than now. Don't ask me why.