I'll be honest: I don't like loudness when it comes to speaking.
It doesn't mean I wouldn't like you, though. I've liked people who speak loud.
I guess one solution would be, like others have said, to monitor the volume of your voice when you're in private. Perhaps, talk to a mirror or something. Or listen to yourself on tape.
I'm usually a rather soft-spoken person---but, sometimes, when I get enthused about something, I've been known to embarrass people in public.
When it comes to how thoughts evolve into words, sometimes I'm guilty of what you're "guilty" of. I get a little carried away. The solution, in this case, is to consciously edit your thoughts for relevance to any topic.
If I actually knew you in person, I might be able to offer better advice.