What could make a cat play in litter every 5 minutes?

she's been doing it now for over a year. first few weeks i thought it was cute,now it's become a nuicanse to be awoke at night by a cat raking in litter litterely every 5 minutes. i change her litter every morning morning and everything looks normal as far as her using it normally. i've tried every other different kind of litter,cause i thought she just may not like that certain kind,but she does it with every brand. and by playing in litter i mean by just in the box it's self stirring it up and kicking it around. is it just a habit for her maybe?