An electromagnetic field is subject to a number of things, including as you suspect, static electric fields. But we have learned that the electromagnetic field - the audio signal carried through wires and cables is also subject to magnetic interference as well as mechanical interference.
On need only look at vibration isolation of turntables, CD players, DACS, solid state and tube amps to conclude that the seismic type vibration - due to Earth crust motion, subways, trucks, etc. - that affects the entire house is making its way up into the component and degrading the sound (without vibration isolation). When the component is isolated from the structural vibration one can appreciate that the vibration must have been degrading the sound.
Perhaps you've seen the experiement when a magnet is shaken the magnetic field lines that normally appear stable and uniform around the magnet become disturbed and move around and can even become detached from the magnet.
In normal operation a capacitor vibrates, thus damping the capacitor reduces the vibration, resulting in better sound.
So, we have acoustic vibration from the speakers to worry about, also vibration generated by the component - motors, transformers, capacitors, etc. - and structureborne vibration that vibrates the walls and floor. The structureborne vibration is a form of mechanical feedback when it makes its way from the floor to the component. Footfalls on wood floors are a good example of this mechanical feedback, or a bus passing over a manhole just outside that causes the needle on the record to jump out of the groove. The vibration of the walls and windows is another problem, producing acoustic signals that interfere with the primary signal from the speakers.
