I too have problems modulating my voice, though for me I usually have the opposite problem - people don't hear me because I don't talk loudly or clearly enough. Others take advantage of this when they interrupt me, if I try to finish what I was saying they just keep talking over me, knowing I don't have the volume to compete with them. But then on occasion, when I get really caught up in a conversation, I realize in retrospect that my voice was probably too loud (although I could be mistaken, since nobody's ever actually told me it is). I also have recently developed a tendency to raise my voice a bit when I'm feeling defensive, especially when I'm trying to talk to someone who I know has a habit of interrupting or talking over me, and in those situations if someone talks over me, I do raise my voice and continue talking because otherwise I'm not going to get a word in, I'm just going to get another verbal beating.
_________________
Yet in my new wildness and freedom I almost welcome the bitterness of alienage. For although nepenthe has calmed me, I know always that I am an outsider; a stranger in this century and among those who are still men.
-H. P. Lovecraft, "The Outsider"