Its interesting in the past,
People would put black tac under components to damp the vibration to components. The idea was to stop vibration and tribo-electric effects, but there was also a hidden issue "the capacitance between a component and something else". ie adding material to a PCB damps the PCB. If this has an effect or not is interesting taking into account that in old valve radios the tuning section was often mounted on grommets.
PCB materials is another interesting point.
Its interesting to hear that someone put a crystal on a circuit board and the sound changed<<really?
So they took it off and it sounded different, so they glued it on the board and it didn't work any more.
I will never forget in a HIFI shop, asking why a CD player was on metal spikes and being told it changed the sound.
After picking myself up off the floor laughing they said listen they played a track then took them from under the CD player and played the same track again. It sounded different, after now doubting myself the assistant had to do the same thing for the next 20 tracks of different CD's I was at a loss to actually believe what I heard. They did the same with a mains cable as well, but that's off topic in this thread.
This is a PITA everyone says its auto suggestion so it must be.
Regards
M. Gregg