At any point in time, do you have a dozen or so book ideas floating around in your noggin? Yeah, thought so, me too! ;-)
I have characters forming and evolving at the weirdest moments. Plots that just pop up out of nowhere, or as the result of a funny headline, a TV commercial, even while watering the lawn. (What if the rabbits decided to arm themselves and take out the coyotes? You know, little bandolier totin' Rambo Bunnies from Hell? Just a thought.)
There are times when it takes all my will to focus on the story in front of me. All those little red-eyed bunnies, alien androids and Octozoids are fighting each other for a chance to say something. It can be pretty loud and freaky sometimes. Kinda fun though. "Hey you, get back in line, stop steppin' on the bunnies or somebodies gonna get hurt!"
So I try to open up outlining files for each idea and just let the voices flow for awhile. That usually clears the racket for a few days and lets me concentrate on book three of the 'Arlo and Jake' scifi series.
All in all it's not a bad 'problem'. It's inconvenient when I want to make progress on book 3, but it's amazing how letting the voices out can clear my mind and add to my growing list of book ideas.
I hope you have figured out how to deal with a crowded universe of characters. Let me know how you do it!
Be the Busy Bee.