I play the French Horn and I know exactly what you mean. It doesn't happen often though. If there is a distinct rhythm before I play the note, it almost never happens, however starting a song without anyone else playing first can trigger it. It's been a while since it has happened now. It might just be that you recently started playing again and that it'll go away by itself the more you play. That's what it seems like has happened to me. Can't say the same for speaking though. If your brass stutter is anything like mine, I would simply suggest taking an especially big breath before that first, risky note as well as thinking rhythmically, that is you don't only think about the specific note but instead the whole song before you play it.