Nowadays, our technology is quite advanced.
So, why can we not make a vacuum cleaner that is quiet?
I suspect it’s hard to make a device whose job is to move large quantities of air through a small area quiet.
However, the bigger issue is that it isn’t so much that they can’t make a quiet vacuum cleaner, as theat they can’t make a quiet vacuum cleaner that’s economically competitive. Would you buy a quiet vacuum cleaner that cost several times as much as a noisy one, weighed a lot more, and did a worse job of cleaning? I wouldn’t.
They are all quiet to me 
BTW, did you see the new one called Roomba? It’s a Robot & cleans your floor for you automatically when you are asleep or at the store. It’s about $200.
I have a Eureka central vacuum and the vacuum itself is reasonably quiet at the power head. Just a whistle of air. But the motor driven brush unit generates a lot of noise. Mostly by virtue of the brushes “beating” the carpet. The power unit is mounted in the garage and it’s loud out there, but then I’m not there when it’s running, so it’s not a problem.
I have no cite for this, so take it for what it’s worth: I heard several years ago that at least one manufacturer had tried making a quieter vacuum cleaner, but that consumers had rejected it during research testing because it was perceived as not being as powerful as noisier models.
The Roomba is amusing, but it’s a lousy sweeper. I would say it sucks, but it doesn’t suck at all. It’s just a self-propelled version of the ancient non-power bissell crumb sweeper.
I think I made an error. The brand of the old human powered sweeper, I think, is something other than Bissell. I can’t think of it right now.
Hoky, that’s it.
I’ve got an antique Electrolux Model G “torpedo” style roll-around canister vac that’s quiet enough to allow conversation in the same room. Plenty powerful and more durable than the plastic stuff sold today.
WotNot, Consumers Union reported that in an article about vacuum cleaners: They could be muffled a lot better than they are, but psychology plays a factor here. Consumer tests have shown that even with all other things being equal, the louder vacuum cleaner will be judged by users more powerful than the quieter vacuum cleaner.
I refuse to vacuum because of the sound. Hubby gets stuck with that particular chore.
Of course, this means I’m not all that eager to buy a quieter vacuum, for reasons that should be quite obvious. 
Julie