The fact that they NEED "cleaned" so damned often should be a bad sign in and of itself - I don't remember the last time I had to "clean" ANY ball-bearing design fan out, they just keep running and running and running and they don't DIE AND TAKE VALUABLE COMPUTER GEAR WITH THEM WHEN IT OVERHEATS BECAUSE THEY DIED VERY YOUNG.
YOU are the one that said "suddenly" - I realise quite well that the gear will usually survive a short while after the fan dies and lets the gear start overheating.
You also ASSUME that I only have 1 or 2 fans running - I can just look behind me and see at least 20, ONE fan going out is not going to change the noise level in my computer/miner gear room noticeable at all.
If a sleeve bearing fan actually LASTED a year reliably, it wouldn't be so bad - but I've had WAY too many of the cheap pieces of junk die on me in a few MONTHS of use, sometimes *A* month of use. They are NOT reliable. They do NOT last. They are shit by design. There is a REASON they are cheap.
Like i said, i clean a few of them over a period of a year, and since i have software monitoring my temps, its very obvious when something has been 10c over the rest for months, its time to clean it.
They make a distinct rattling noise, just like the delta you favor so much when they get dirty. I have such fans at a different location too.
When one fail its not like its going to damage the miner either, every single miner app has temp protection, and it should not get that far anyways considering you have months to clean it when it start under performing. Also the fact i have 2 to 4 fans on every different miner and RPM is tracked on all of them.
If you want to use noisy fan, thats all up to you, but that does not make my choice of keeping my mine in the 30-40dB range a shit choice.