My 14 year old does this very often, and it's very annoying. At first I assumed she might be coming down with something, but she never got sick. I asked her if her throat is sore, and she says no.
I attempted to point it out to her every time she did it, to try to find out what brings it on, but her reply is always the same..she doesn't have the need to cough, no itchiness, no soreness,.. nothing! She isn't even aware she did it.
I can add that it is never at a specific time, like only after eating, drinking, etc. She also has been seen by the family physician, which said she's in perfect health, with the exception of bad sinuses.
I've come to the conclusion that it's somehow an annoying habit that she has no explanation for, or it due to her sinus problems..drainage.
That being said, has you husband been seen an ENT?
It could be sinus drainage.