It can be one of many things: laryngopharyngeal reflux
(stomach acid coming up to the voice box), post nasal drainage
, dryness, a weakness of the superior laryngeal nerve
(the nerve that gives sensation to the voice box; usually viral), or even wax in the ear
canal (there is a tiny nerve, arnold's nerve, that gets irritated and triggers a cough
via a tickle in the throat).