Even if you managed to go the entire minute without subvocalizing, it probably didn't feel like the natural way of things. It probably took effort, and possibly a great deal of effort. But I predict that most of you didn't get through the whole minute in total subjective silence. (If you succeeded and it did feel like the natural way of things, I'd very much like to know.)

Does playing wordless sounds in your head count? I can't quite shut off my inner audio stream at will, but I can concentrate on, say, a clock ticking, although instrumental music is much easier to focus on. Another time it turns off is when I'm playing a video game and frantically reacting to things without stopping to "think" about what I'm doing.