I realize that the reason you need to be so loud is because you are so big. I do not, however, know the reason you need to be so big.
If cities didn't have fire hydrants, I could understand that you would need your ear-splitting, gut-rumbling 56-cylinder engine (or whatever) to quickly carry hundreds of gallons of water to the site of a fire.
In a world where modern technology hadn't rendered ladders extremely collapsible and compact, and firehoses capable of being folded and coiled to the point of being almost nonexistent when not in use, I might see a reason for you to be sixty feet long and weigh 9 million pounds.
If the majority of emergency calls came from halfway up Mt. Rainier and not down nicely-paved city streets, I could even let the logic behind your behemoth off-roading wheels slide.
If this weren't the richest country in the universe, maybe we couldn't afford to develop the technology to suitably dampen the racket produced by our state-of-the-art, top-of-the-line response vehicles.
But since all of these scenarios were just made up by me, Fire Trucks, perhaps you could stay in tonight so I can enjoy having the windows open. It's nice out and you're ruining it for me. We have plenty of buildings. Let a few of 'em go. I can't hear the movie I'm watching.