What is my clown doing?

[lastlight]

I have a female Fire Clown in my 34g. The past few days she's been settling on the sand and then flipping her tail like crazy. She clears out little areas of sand like this until the glass is exposed. It's raining sand all over my corals. This is not an irritation issue...she looks fantastic and eats like a beast.

What's up with this? Anything I can do to stop it?!