Wow, I thought I had heard everything, but that's a new one. I certainly don't think normal conversation of any volume would create enough movement of the drivers to cause any back EMF, especially without an electrical signal entering the cones.
Is it okay to talk around your speakers?
When a system is not on, should you avoid making any noise near the speakers? I am thinking about back EMF caused by the speaker cones moving and then sending voltage backwards into the crossover and the rest of the system - could this cause damage or even minor degradation to the sound quality after a while? Do you unhook the speakers when not in use just to be on the safe side?