I've been hearing the strangest overtone in this piece. I haven't had a chance to try it on any piano other than my own, so it might be that mine is just out of tune enough to cause this to occur. Perhaps one of you is working on this, or has encountered it before.

Leaving the middle section and returning to the main theme on the last page, F above middle C is held by the left thumb for 3 measures into the next section. The open F doesn't sound throughout, but is replaced at some point by overtones/sympathetic vibrations that do not work with the piece at all, in my opinion. Does this happen when you play it? Could Chopin have wanted this ghostly sound in the midst of this piece? Any thoughts? (If you don't know the piece, it's available for free from Sheet Music Archive and it's one of Chopin's best.) Thanks.