A lot of writers start interviews with jokes that come directly from the voices of their characters. It sounds a little crazy but I hear my characters' voices in my head too. More specifically, I hear dialogue, usually entire chunks of conversations. It can be distracting when I'm at my day job and trying to concentrate. My characters can get pretty insistent.
Sometimes the voices help me out when I'm stuck. For example, this past weekend I was struggling with the opening scene of the third chapter of Quads, the first book in the Living Little Women series. In the scene, Sarah, my narrator, is going to her first bike race. It's a very important scene because Sarah is supposed to fall in love with the sport. But telling it from her perspective wasn't working. The problem was that a lot about bike racing needed to be explained, but it was implausible for someone to know all that at her first race.
Then I heard the voice of another character:
Stefano Bennati should have been out racing his bike that morning but due to an unfortunate incident involving Newton's Third Law and a jackass who didn't know how to handle his bike, he was standing on the side of the race course with his arm in a sling.
Sarah needed a person like Stefano, who is the captain of the team and who has been around bike racing for a few years, to explain what was going on. From there, the story flowed logically and I was able to switch back to Sarah's perspective a few paragraphs later, once I got all of the basics down.