I was going to say posible urinary infection/blockage, but if he's been doing it all week he'd probably be very sick by now. It probably wouldn't hurt to have it checked at the vet. The reason I guessed that is because when my late kitty Boo had a blockage he ran up and down the hall meowing, going back and forth to the litterbox. I think he was telling me something was wrong, but I was too stupid to pick up on it. I did manage to pick up on his hints in time to bring him to the vet's and get him unblocked, but I wish I would have recognized the signs sooner - I feel bad for not noticing right away that something was wrong.

Some kitties arejust naturally talkative, but if you think it is abnormal it might be something to get checked out.