Obsessed with covering up in the litterbox!

My 1-1/2 yr old cat is overly obsessive about scratching in the litterbox, both before and after use. It drives me nuts to see him so OCD about it. He can spend close to ten minutes in there! He has done this since he was a kitten. I attributed it to being in a rolling cat cage for a good part of the day when he was young. Figured he was bored, and that gave him some excitement. He does not do it excitedly anymore though, just seems OCD. I have had him on several different litters, including walnut litter, though I have not exhausted all options. Any suggestions or insight?

If he's not throwing litter everywhere in the process it might be best to just let him be. Cats have comfort rituals and good litter box habits are to be admired. If you try to change those habits you might end up promoting litter box avoidance.