There was a fluorescent street light installed in our town having two 20W tubes in it. It did buzz very loud that one could hear it by walking underneath of it. The ballast was a two lamp resonant start type and it was not screwed properly onto the gear tray and additionally it was having an issue with loose iron core.

Hmm... probably the 2x 36w fitting that used to be in my uncle's kitchen, or a few of the 4x18w fittings at my old school. There's a mercury street lantern near me that's loud too, and once I heard a really really loud wallpack on a school building... it appeared off too!

[...] and once I heard a really really loud wallpack on a school building... it appeared off too!

I've seen (heard) that, too. I believe it might be the ignitor pulsing continuously that is making more noise than the ballast would. The ones I saw (heard) were older HPS and I believe they didn't have "smart" ignitors with a timeout.