Even John Palmer includes it in How To Brew. I am assuming it is in the book, although I do not have it handy - but, it is on the web site at the beginning of Chapter 9:
What we need to do now is transfer it to your fermenter, make sure the wort has been aerated, pitch the yeast, and find a quiet place to put the fermenter for the next couple weeks.
From a scientific point of view, sounds travels through waves. The varying frequencies and amplitude of the waves cause sound, which is just what we perceive through vibrations picked up by our ears. As sounds are simplified as being vibrations, there is some degree of vibrations picked up by the fermenting vessel.
From a logical point of view, I would imagine that there are a few possibilities for creating high levels of vibration, some of them sound-related. It would take a massive source of vibration to cause that to happen to such an extreme, though, and the net result would be some degree of agitation to the vessel. The amount of a disturbance to have an impact, if there even is one, would come from something so loud that I doubt any of us will ever encounter. So basically, don't put your fermenter on top of your home theater subwoofer or half-stack guitar amplifiers. :-)
I would imagine that "quiet" is more an attempt to imply that it is somewhere that would not be prone to bumping into or experiencing wild swings of lighting and temperature.