What is a soft, involuntary "hu" sound on every exhale a symptom of?

I know two promiscuous women who make soft and slightly forced, yet almost involuntary, "hu" sounds everytime they exhale. I would like to know what that behavior could be a symptom of? One I know has diabetes and her feet have cracked skin, nasty toe nails, and sores. The other woman has the same look to her feet but i don't know if she has diabetes. So my question again is what could possibly making them have that sound when they exhale ( STD, Diabetes, or something else)?