Thank you!
I did both things. Switched left and right locations, and looking inside. Everything is intact inside, and switching positions helped me figure out what happened. I just put it in writing so that perhaps someone can benefit from this later.
-- During the day I had been trying for the first time some new headphones for my mp3 player. They were really bad and I think they left me with an extreme sensitivity to the sound of the tweeter. After a couple of days, the sensation is gone.
Thank you for your suggestions. So great to have this community of audio enthusiasts!
Fernando