Sissy has a habit of pawing and scratching at papers like letters or bills left on the counter, and boxes like empty cereal or cracker boxes. She really gets into it, scratching away like she's in the litter box.
I know it would be great if they could explain their strange behaviors to us! lol. You may be onto something with the stress and frustration think. I've noticed she does it when she seems restless and looking for something to do so maybe she does it out of boredom.
My cats do this too (well, one of them anyway!) I think it's a way to re-leave stress or frustration. My older cat does it on the door when he wants to go out and everybody ignores him. It may just feel good. I wish they could tell us!