If the sympathetic vibration of piano strings is significant for quantum mechanics theories, you are doing something wrong. This is a wholly classical physics phenomenon.
Sympathetic vibration is actually a rather standard phenomenon. I has happened to me repeatedly when practising singing that I was annoyed by some buzz that turned out to be, for example, some pencil in a metal container on a writing desk. Finding the culprit of such sympathetic responses may be tricky.
Now a buzz is noteworthy because it is a non-linear response containing overtones not present in the exciting vibration. The whole room usually responds in a linear manner that one does not realize until one has actually sang in a sound-deaf room without reflections. Reed and brass instruments work principally by using a sympathetically vibrating air column in resonance with the actual sound production (reeds or lips).
It is pretty easy to get sympathetic reaction from a piano by putting down the sustain pedal (thus removing the dampeners from all strings) and singing into it, or knocking on it.
Without using the sustain pedal or holding down the keys for the resonating notes, you'll notice much less of an effect.