As mentioned in an earlier post, you might check your enlarger for light leaks. In looking at your enlarger table setup, I'd also suggest painting the walls and ceiling surrounding your enlarger flat black. Any light leaking from the enlarger and bouncing off the walls will contribute to fog. Light from the lens bouncing off the work surface and the walls will contribute to fog. So will burning in a print with a hole in a card that has a white or other reflective surface facing the paper. Use only a card that is black on both sides. This may all sound pretty picky, but if following any or all of these steps reduces stray light by only 5%, you've reduced potential sources of fog.