I don't have any advice....sorry.

Molly is the same way, except it's excessive barking. I don't blame her when she barks at people walking by, coming to the door, etc., but when it's just at nothing...it can become pretty annoying. She's not bored, not outside for the whole day; so I'm guessing she's just being a typical Collie. Most of them are barkers. I also refuse to get her de-barked or wear one of those collars, and so do my parents. Daisy is usually quiet, and only really starts barking if she's playing or sees a squirrel/bird.

I hope you can figure something out. Good Luck.