The bq witbox is quite loud out of the box. Initially I had some filter pad taped on, but that didn't stick too well. So here's a solution. Customisable to fit any fan, so not restricted to the witbox. The filter doubles as silencer, bringing down the fan noise roughly to the printing noise. (Depending on the choice of filter pad) Print one per fan, remove the fan mounting screws, place the base flush with the printer and put the screws back in. I think most of the dirt in the filter comes from outside the printer as I'm not vacuuming that regularly... The level of filtering obviously depends on the size and filter choosen, so no guarantees whatsoever for using this design: http://spectrum.ieee.org/nanoclast/semiconductors/nanotechnology/nanoparticles-emitted-from-3d-printers-could-pose-a-risk