Rubbish, that's your opinion only.
There will always be a "It never happened to me so it's not real" school of thought. Also the "cheap" adjective eliminates a lot of fans. The cheap ones don't have the extra control ICs that eliminate the PWM sound
PWM click and humming has been well known "feature" of PWM
http://www.silentpcreview.com/forums/viewtopic.php?t=9340
https://www.ekwb.com/blog/what-is-pwm-and-how-does-it-work/
More quality fans have their own special IC driver chips within the motor hub that generate a sloped PWM signal instead of a flat square one. Flat square signals tend to create unpleasant clicking noises when the fan runs at low speeds. The sudden rise of power when the motor is given +12 volts results in the rotor being jerked, which in some cases creates the clicking sound.
Newer designs, even MoBo utilities, incorporate ramp up and down times. For my build, I ramp the fans up rather quickly in response to rising temps but ramp it down over some 90 - 150 seconds to remove latent heat from coolant. Because of newer fan designs the problem has become less and less over the years. However now we can use PWM fan control PCBs to power less expensive 3 pin fans for less cost and eliminating any PWM noise issues.... the proverbial "best of both" worlds".
Anyone interested in the topic can use a search engine for plenty of descriptions, mitigation measures etc.
https://www.google.com/search?q=pwm+noise&ie=utf-8&oe=utf-8&client=firefox-b-1
https://www.instructables.com/topics/How-to-eliminate-PWM-noise-at-slow-speeds-when-usi/
http://www.silentpcreview.com/forums/viewtopic.php?t=9340
http://educypedia.karadimov.info/library/00771b.pdf
As previously explained, PWM acoustic noise is caused by the impulse torque generated by the fan motor during each active PWM cycle. Reducing this acoustic noise involves slowing the slew rate of the PWM switching, thereby “smoothing” the PWM impulse torque profile.
There's also a hum that is sometimes at low speeds caused with EMI related ...
https://forum.duet3d.com/topic/3590/pwm-fan-noise
I haven't experienced it personally in 10 - 12 years... but we stopped using PWM about 5 years ago. Before that, it was just a matter of either using the right fan or using ones with the "bump" in the cable which had the "thingy" (it's a technical term), that eliminates the noise. You'll see it dsicussed mosatkly on water cooling forums where folks are running a number of rads, oft in push / pull where the mind set is more fans running at lower rpm than less fans running at higher rpms. You are certainly not going to see it on a CLC with fans at extreme speeds. These days, you generally have to get down to 300 - 450 rpm.
As for fan orientation....
front = Intake
rear = exhaust
bottom = intake
top = it depends
If you have 1.3 (Im an anal about cleaning my fan filters kinda guy) to 1.5 (I'm kinda lax in cleaning filters) times as many intakes as exhaust, then top fans can be exhaust. If you ignore this....
a) You will have negative case pressure. and no, dust is not the big issue here.
b) with neg/pres, air has to get in somewhere ... most often that is thru vented slot covers and those large holes on your rear case grille.
c) You can easily test this w/ a $39 garage band fog machine from Amazon. When you do, exhausting the fog between the wall and your case rear, you case immediately fills up with smoke.
d) when you watch the smoke being sucked in, start thinking about where the air is coming from . It takes a few seconds but then comes the light bulb ... my 300 watt GFX card is exhausting right there .... my 750 watt PSU is exhausting right there. Intake air will follow the path of least resistance.... so it's going to go thru those big vents and holes at the rear a lot easier than it will pass thru your dust clogged air filters.
If you don't have that many intakes, then top fans should be intakes. If you have radiator, rad fans are always always,
no exceptions intakes. This is the 2nd law of water cooling... 1st is never mix metals within the loop. Even tho CLC sellers violate the 1st rule, they don't violate the 2nd rule.
https://www.corsair.com/us/en/Categ...00i-PRO-RGB-Liquid-CPU-Cooler/p/CW-9060033-WW
Page 4, Panel 3...
Attach the radiator and the fans as shown. For the best cooling performance, we recommend mounting the fans as an air-intake to your PC case.
I liked saying this better when I had Gentle Typhoons on top of the case, and when Id hear what we all learned in 8th grade earth scienc that hot air rises.... no not in a room with a ceiling fan and not in a case when the Typhoons are blowing the other way. If not convinced, spend the $39, grab the fog machine and blow the fog behind ya case ... then watch it fill up with fog. And no, the heat will not get trapped inside... with 2 fans on top, 2 in front blowing in, the elevated pressure inside the case will push out all the hot air inside the case thru the path of least resistance.... those rear grille and slotted covers, taking all the heat out at a rate of around 2 full case vlumes every second.
Think about it this way .... ever use a window fan to cool down a room... do you install both an intake and exhaust fan ? or just use 1 fan and open a window ? Will it be cooler if you use the fan as intake or exhaust ? Neither. Have an exhaust hood over your stove ? Does it have an intake fan ? Well if ya didnt suffocate from lack of oxygen, then an equal amount of air must be entering the kitchen. In any enclosed space, the intake will always equal the exhaust.
the others are all good?
