Where do ideas come from?

When I remember last night's dreams I can exactly trace the origin of some. A recent movie, conversation, or unexpected event had something of a makeover. Then the edited version reappeared in my dream, either as a snippet or major theme. Others come from some unknown, baffling sector of my brain. So it is with ideas. Some are the product of a logical progression toward a goal, flowing from a predictable thought process. But occasionally, some bizarre idea comes hurtling out of nowhere to implant itself and disrupt all that tidy mental order. Where do those ideas come from I wonder? Are they like radio waves, floating through the atmosphere, waiting to connect with the antenna of my mind? Do they pre-exist inside, waiting to be mined and brought to the surface? Or is there a busy little factory somewhere inside our heads--or maybe stored in the cloud--generating ideas, dreams, and notions for my rational review and approval. If a thought feels ignored, will it then burst forth in my dreams? I wish I knew.