No, this isn't an electric piano that I set to piano + guitar.
This is the same upright piano that I have played on for years.
While I was playing Fur Elise, specifically the section with no left hand rests, I heard a twang coming from one of the keys, not sure which one but I am pretty sure it was in the treble clef, specifically either the high end of the first octave or the low end of the second octave.
It sounded like a guitar string was plucked hard at the same time that a key at the same exact note was pressed at forte.
Does that mean that I just broke a string on the piano? And if so how could I tell, lack of note when I press a key?