There is a rational reason, as such, for the phenomenon you experienced but few understand it or believe that it's possible.
More and more people are beginning to experience these very strange occurrences all over the world. These effects is a signal that the old world ideas of religion, individualism, and nationalism is on their way out and a new world order is about to emerge. Unfortunately for us all, the approaching new world order is far more evil, demanding, and restricting than that of individual nations. The world is facing some very hard and difficult times ahead. There are secrets to life and nature that those who run the world governments and control the world's population of human beings have not told us about. There exists classified technology that operates in undreamed of ways that defies the natural laws of physics. This technology could be used for the benefit of all of humanity, but instead it is being developed and used to control and manipulate the lives of people around the world, to enslavement. That voice coming out of the unplugged radio, if you listen closely, you will not be able to determine much about what is being said, this is by design. The sounds you hear coming from the speaker is sounds that are almost words, but not quite. It is a type of programming that the subconscious brain can understand but completely befuddles the conscious mind.
There is some kind of projected "tune" that people are hearing at home and in public places that also comes out of anything that has a speaker in it, turned on and operating or not. People at places of their employment have heard this phenomena and, they will either pretend not to hear anything or they will acknowledge it and then explain it away as: well, its AT&T up dating their remote repeater sites. I, for one, know better. If people don't wake up and take a serious look at what's going on in the world and who the movers and the shakers truly are, people are going to end up mind control biological robots willingly serving their one world masters. And that time is very, very near.