I rarely have internal monolog, but instead have an internal dialog. Most of the time I'm explaining ideas to people, sometimes arguing with them.

I've found this is how I think through things. "Talking" things out with the various models of people I have in my head can be useful...

I've found when there isn't conversation happening, its typically replaced by music. I can hear and play songs perfectly in my mind. Listening to music with headphones helps turn off the conversation so I can focus on other tasks more fully.

I used to be concerned I was crazy for having these dialogs, but, I get along ok. :)