What Is The Cause Of Change Of Voice?

I first thought my 29 year old son had a cold affecting his voice. Then I noticed everyone sounded weired. But especially those, male & female who had deep voices. The lower the frequency the more they sounded like robots. It reminded me of robots on Star Wars. I knew something was wrong with me. There was no pain so I didn t do anything but simply hope it would eventually clear up. Well, it did to a degree, but I have reocurring bouts that randomly appears. I turn 60 this month and obviously have adjusted to bodily changes though the years. The onset of this was quick, one day normal the next day robotic voices. What is the cause and what should I do?