Great question. Many years ago, I was on the western apron at Moorabbin Airport when a Mitsubishi MU2 taxied, parked a short while (with engines running) then taxied away. The noise was absolutely unbearable; you really couldn’t be out there without HAVING to cover your ears.
Coincidentally, check out this article on XF-84H ‘Thunderscreech’
https://en.wikipedia.org/wiki/Republ...Thunderscreech
It was an early (1950’s) turbo prop. The tips of the props exceeded the speed of sound AT IDLE! This was the loudest plane ever produced, and could be heard 40 kilometres away. A short read, but well worth it!