Hi Janer In my experience, the usual form of this is 'think out loud', or 'thinking out loud'. Here's a couple of examples: 1 - When you hear someone mumbling something to themselves, you might say to them: "I didn't hear that; did you want to say something, or are you just thinking out loud?" 2 - Sometimes it is used when people are exchanging ideas or considering options - you might say "I'm just thinking out loud, but what if…..". You would use this when you have an idea that might not be worth mentioning, but you are doing so anyway in case it is relevant.

They are interchangeable, just like "round" and "around". Ex. I was thinking aloud/ I was thinking out loud. Depending on where you come from, either one could be more common than the other. So use whichever you please! :)