Strange empty folders appearing in windows network?

On our network at work, there are folders that appear inside of other folders. No one is creating the folders and the folders are empty. We delete them, and they'll reappear. The folders are usually named "15" but we have also seen "12," "13," and "14" too. Our IT person says that she has no idea what these folders are or how they're getting there. Does anyone have any idea what these are, how they're getting here, why they're appearing and how we can stop them? Thank you!