So when we got my cat his first closed litter box and we would always hear this digging sound coming from it! we were sure he was just covering after himself but turned out he was scratching the walls of the box! till this day he still does this and he can go on for 10 minutes until we call him out! Now I've been searching for info about this behavior and only found info about cats pawing\scratching the air in their litter box, but he actually uses the walls to file his nails, I must mention he does not scratch anything else in the house, in fact he does not use his claws to attack either (people have asked me if he was de- clawed before! )... non of my cats ever did this and I've never seen a cat do this so I don't know why he does this, it may be that's just where he likes to do it but it just seem's really odd to me ! did any of you ever hear of this or have a cat that does this? I've just always wondered..