>Why do you say it's not?
Because it's not, harassment is usually implied to be personal, involving hostile contact between the harasser(s) and the harassed. Did the protestors shout insults or threats at you or other neighborhood residents ?
>all illegal under existing laws
Do we really need to constantly circle back to the point that protests have to be lawful ? they do not, protesting is about breaking the ordinary and disrupting the status quo, that's the point, especially when the people protesting feel cornered and without a lawful retort to perceived injustices.
Every action against the government will hurt the population to some degree or another, 100db noise seems pretty mild compared to the private property damage valued in the millions that large-scale protests usually cause. Prioritising comfort over protest is implicitely siding with the government, which is your right off course, as long as you're explicit about it.
Edit : 100db noise turns out to be a deadly serious matter, I apologize to the person I'm replying to for making light of it.
I still believe it's wrong to use this as justification for quashing a protest, there is a whole spectrum of solutions from reasoning with the protestors to wearing ear covers, but I can better understand and empathize with the antagonism most of the affected city's residents hold toward the protests.