No, you know perfectly well what you are talking about. Listening again to this without earphones with my wife we both heard this pulsating hiss. Maybe my error was to edit the MP3 and not the WAV file. I shall try again.
Keep in mind mp3 is a compressed, "lossy", format. When you edit an mp3, the audio software first has to expand it to a wav, which is of less quality
than the original wav - because what has been lost never can come back. You edit the wav, then compress it once more to mp3, losing even more quality. You see why editing an mp3 is not a good idea.
But interesting you could hear hiss without headphones which you could't hear WITH them. Usually it is the other way around.... Are you sure it was not somebody taking a shower or hosing the garden ?