All good points. I would say that it's a fairly outlandish scenario where you are (i) close enough to the device to listen to the caps whining but (ii) can't measure actual voltages within the circuit (which could be a lot more informative) and (iii) can't just listen to the audio output of the device directly.
Acoustic noise is one thing, but it's not at all outlandish to be within range of the EMI emitted from the same power supply which tells the same tale. What is outlandish is thinking anyone bothers listening in. :)
