I recently acquired two USB 3.0, 2.5", 5400 rpm external hard drives ($69 each). They are the quietest devices I have ever used. If were not for the flashing blue activity light, I would never know they were operating.
The trade off is that they are not particularly fast. I think that is more a function of the 5400 rpm, since USB 3.0 is speedy. I think the combination of slow/speedy makes them usable in my situation.
On a Mac since 1984.
Currently: 24" M1 iMac, M2 Pro Mac mini with 27" BenQ monitor, M2 Macbook Air, MacOS 14.x; iPhones, iPods (yes, still) and iPads.
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