Even worse, it wasn't just truck horns. There were several trucks driving around with train horns installed. And plenty of the apartments in Centretown are right up against the street.

I don't think making 80+ decibels of noise 10 feet from people's windows is even an okay way to protest, no matter who you are or what your cause is.

I used to live in this neighbourhood, right by Somerset and Metcalfe. Protests happened all the time. Some of them were anti-government, even. And none of them launched this kind of sustained assault against innocent citizens. I get the sense a lot of them think they're sticking it to the liberal elite, or something like that. But really - Centretown is (or was when I lived there, at least) one of the more affordable parts of Ottawa.

80? I had heard in some cases it'd been measured at up to 140dB.

I wouldn't doubt that for the train horns, especially outdoors. ~80db inside an apartment is what I heard personally from someone I trust who lives there still, so that's usually what I go with.