[Al Skierkiewicz]

Aaron,
The terms "microphonic" or "microphony" imply that the device is receiving acoustic energy and converting it into a signal, or noise and distortion in an existing signal. In the cases I was describing, the components themselves are reacting with the surrounding air or vibrating parts within the component to produce sound. In the case of magnetic devices like transformers or motors, the changing fields in the audio spectrum can either move the parts of the device to produce sound or move the entire device to produce sound. It is not uncommon for a transformer winding to become loose on it's core and vibrate at the frequency (or sub harmonic) of the signal that is passing through it. Capacitors have been known to also produce sound, particularly those that have aged and have microscopic spaces between the plates. As has been pointed out, ceramic capacitors have a slight piezoelectric effect and can physically distort with applied signal.
High quality audio transformers take care of many of the problems related with transformers by dipping the cores in a some adhesive (usually a high temperature varnish), using specific winding techniques for the wires and then securing all components of the transformer so that nothing moves when it is installed. In some transformers it is also necessary to enclose the transformer in a magnetic shield to prevent magnetic coupling with other components in the same equipment.