I have the machine with the little filter about 1 inch by 2 1/2 inch. The smell is not constant. It is not like a dirt or dust smell. I replace the filters often which helps for awhile. I bought more filters in case my others were too old. I clean everything often enough.
I am now thinking that the smell is from the finish of my end table where I keep the machine. The smell is very hard to describe. I describe it as metallic, but it really might be the petroleum based finish of the table.
It is in my lungs and I can smell it during the day as I exhale. Tonight I am going to put in a fresh filter and get it off the table.
Has anyone had this problem or guess what I might be dealing with?