Keep in mind that you are supposed to clean the prefilter every six months or so. As for the tip about cleaning those rows of holes, compressed air works really well, but you want to do it outside! And if you look up into that piece from the bottom you will see about 8 large holes that I assume are where the vortices are formed. You will find dust caked all around that area. Again, compressed air makes short work of it, but this really puts out a huge cloud of dust. After doing that, the exhaust from the vacuum will have a lot less odor. I'm guessing that dust may contain pet dander from our dog.