What in the world is Thunder

In book #4, I have added “thunder”, but no rain. Pok’along, Ground Hog, and Charlie have no idea where it’s coming from. No one in the Valley of the Digadoos have ever heard thunder in their valley. Even Maetoo, the head of the council, can not offer an explanation of it’s source or purpose. What do you think it will be? Is this a door of change that has developed? I’m interested in your ideas of what it can be. You could be quoted in this, the new book that is in progress.