Why did the Chinook Helicopter blades all break the sound barrier in 1992 over the city of Mt. Shasta?

Mt. Shasta city is at 3500 feet to 3700 Feet in altitude. Then the helicopters had to fly at least between 5000 and 6000 feet altitude not to crash into the ground and to have enough leeway between their cruising altitude and the ground to allow for up and down drafts (especially in the vicinity of Mt. Shasta the mountain next to the city). Because Mt. Shasta is known to create all kinds of extreme wind conditions especially the closer you get to the mountain itself. Winds come and then had to find away around or over the top of the mountain which can create more treacherous wind conditions on the mountain. many Hang glider enthusiasts and paraglider enthusiasts have died because of this trying to fly their kites with their bodies on board around the mountain because of these potentially treacherous wind conditions by the way.

So, in order not to crash they had to up the speed of their rotors because of the altitude and this created (as they moved forward the forward movement combined with the speed of the rotors the "BANG! BANG! BANG! BANG!" of each rotor tip hitting the air in the front of the helicopter moving forward which sounds a lot like someone hitting metal on an anvil: "BANG! BANG BANG! BANG! and so forth.

However, these same deafening sounds caused me to stop washing dishes by hand because there was no automatic dishwasher in this very old 1925 or older house on Oak Street in Mt. Shasta on an acre of land.

I've driven there recently and the house is now even 30 years older and they have cut down the Black Walnut trees and the huge 100 year old Black Cherry trees but otherwise it looks similar except they have finally torn down the old very old Garage that I assembled Sleigh bells to Leather straps that I sold at that time to People with snow sleighs and put the sleigh bells on their horses all over the U.S. at that time. This was one of several businesses that we owned then 30 years ago now. My wife and I still own one business today but it is a different kind of business then then. In my late 40s my life became much better economically.