Thinking Inside My Head vs. Thinking Out Loud

I’ve noticed that I am able to think inside my head (i.e. not talk to myself) great in the car on the way in to work. When that happens, I use my turn signals and do everything else that I’m supposed to be doing. Shortly after I get to work, probably as more people start to arrive and noise picks up, I switch to what I refer to as ‘thinking out loud’. So, is it the noise of people talking around me that causes me to do that, trying to clearly hear my own thoughts? Or is it that when I’m alone I find the idea of my voice breaking the silence disturbing so I think inside my head? Inquiring minds want to know ….