She is showing signs of voice strain. If you know it is not from mike problems or for speaking too much, voice strain occurs when someone speaks to long or two loads in a low register to show authority in their voice and also when someone is aggressive pushing their points at their audience.
There were little personal ticks in the video I watched of her on you/tube were Hilary Clinton announces run for President. Particularly interesting was something she did in what you would assume was a well planned, and you would assume well rehearsed and coached speech. As she says makes the statement, “...and let’s definitely talk about how every American can have quality affordable health care. “ The statement is an affirmative positive statement,”American can have, but her head shakes back and forth in a no as she says “… every American can have..” rather than up and down. This is a subconscious "leakage" cue that signals she doesn’t believe that statement is true. In this same video she also presses her lips together to suppress or pull back from an angry grimace after she says, “George Bush.” This seemed like a planned little act rather than a natural catching of an inappropriately negative reference to the president. Her paralanguage and facial expressions shift from forced and false warmth to what seems more natural derision and sarcasm as she talks about Bush or the current administration.
One of the things that Hilary battles against as a female candidate is that men are uncomfortable around unsmiling women. Which explains why women typically smile more than men – Women maintain community by smiling and men maintain dominance when not smiling and when Hilary does not smile she is showing what many might read as inappropriate dominance.