Flour trick in basement unsuccessful.

   You recall , a few days ago, I spread flour over much of our basement floor, hope to discover whatever has had my younger dog upset on at lest two occasions. I checked it out yesterday. No sign of anything in the flour, not even mouse tracks. As I was writing this, the thumping sound was again heard. The computer time said 7:02. This mysterious sound is like an itch you can't reach. If it has a physical source; I've failed to locate it.