https://www.amazon.com/gp/product/B071SLFBNY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I agree that noise frequency and mounting can make a difference.
I sampled a few other fans from other (cheaper) suppliers; none were as quiet for my uses/preferences as the Noctuas (some were close, and ok as Just Fans, but not audio rack quiet).
I also use one of the 200mm Noctuas as a desk fan, mounted in one of these, whose motors die young, and powered by a Milw M12 battery
View attachment 64029
Noctuas come with silicon sleeves over their mounting holes; I did not use bushings on my 1/2'" plywood 12x20" 'fan' doors, and resonance is not an issue for that. (But haven't measured it, either
I've really not experimented much between auto and smart mode; turns out in my rack apparently I over did the cooling capacity a bit - as I'd intended. I also have not thorougly explored best/hottest placement of the temp probe yet, either (same reason), but expect to be doing some re-racking soon, and will do it then.
Aquaero looks
wild - good do know! ...but pricey. I have a similar but really cheap controller/sensor/display on my big PC's cooler, but is mostly unreadable even 5 degrees off axis, so largely useless.