What Causes Hoarseness In My Throat?

At age 40, I started having a hoarseness condition in my throat that has been on-going for the past eleven years. As a western trained physician, with easy access to medical specialists, they attempted to isolate the root cause(s), with no measurable result. The only symtoms associated with my condition is simply a dry throat. I don't smoke, chew tobacco, use recreational drugs, and I've not been on any medication that might have caused this problem. On average I drink six glasses of water throughout the day. Your thoughts? Thanks :)