Why does my dog act this way?

I have a 5-year-old Australian Shepherd/Border Collie mix. Recently, she's started running up to where my cats are lying, snapping near them, and then running away. She'll repeat this a few times, but only when she's excited, such as before mealtime or when she's about to go outside. It doesn't happen all the time it's mostly around feeding time.
She gets plenty of exercise and has a job, and otherwise she's very gentle with the cats and leaves them alone. Does anyone know why she might be doing this, and how I can get her to stop?