Just a random thought tangent...
The base Individual target for Imagonem is... "...the equivalent of an adult human being; whether a visual image about that size, an auditory illusion making that much noise, or whatever." [size=85](emphasis added)[/size]
If "part of a single noise source" were being silenced, that would need "Part". Even if different sounds from the same person, that is not relevant to "Individual Imagonem" - it's the equivalent sound from one, not the actual sounds from one specific Corpus-type individual. So 20 people whispering might still be "one individual", assuming 20 whispering is not more noise than one person shouting. (Or do we disagree on that premise?...)
If two people were talking in low tones, would that take two Silence Spells, or "Target:Group", even if that noise is less than "one individual", as defined above? What if a mage just wanted to silence the voice - would the rest still make noise, clapping or running? Would that require "part", or is the target "the noise of the voice", and not the rest?
What of the other way around? If a mage wanted to make a person's footsteps and clothing silent, but allow them to speak if they wanted to - would that take "Target:Part", or not? They're certainly different noises, not the same, not the same source, not at all. (shoes on the ground vs a voice.)
The spell is not targeting the person, it's just targeting some of the sound they make. And if you're not worried about the sound of a voice, just the rest, why target it?
Or do we apply the assumption that "one person is an individual is an individual is an individual, sound or body or mind", and let it go at that?
This sprang from the thought to silence only running footsteps. At first I thought: "It's a tiny spell, two feet, two castings, no problem..." - but those obviously create less sound than "the equivalent of an adult human", so why not just silence the "lower half", legs, feet... so why not everything from the neck down? And is that then a "part", or just "one individual lower half", smaller but still individual?