Uromastyx lizard has started digging?

I've had my Uromastyx for about 7 years now and just very recently he started digging in his tank. Like, actively burrowing under his shade log and kicking up a mound. I know some kinds of uromastyx are diggers (namely the Mali variety, which I think he is), but in all the years we have had him he's never done this. What could be going on?