Every time my pro air hfa inhaler gets weaker, I get a little wheeze that you can only hear when I'm in a quiet room (end of exhale).Why?

Return inhaler. Pro air hfa should deliver the same quality and quantity of albuterol with each actuaction until the counter reads zero. If you believe the inhaler is defective, return it to the pharmacy for a replacement. If you find that you are having symptoms that are not controlled, check with your doctor.