I can't help much. I've only had one chin fur chew, but it was extremely obvious what her problem was, and therefore was easy to stop.
Has the humidity where you live been lower than normal lately? If so, this could caue Andy's skin to dry out more than usual. You could try cutting back to one dustbath a week for awhile and see if that helps. Also, what dustbath are you using? Maybe you could try a different brand and see if there is any improvement. If you got it at the petsore, I assume it's not Blue Could or Blue Sparkle, so you could try one of those brands.