Cant remember if anyone already said it...
To get the CPU fan rpm/noise a little less intrusive (annoying) you can insert a temp delta (delay) of 3~5°C in responsiveness of it.
This can be done from a software that you may use to set the CPU fan curve, or from BIOS (for FAN curve and delta/delay)
I do something similar. All of my various builds' CPUs are water cooled, mostly AIOs and one custom cooling loop.
I use a slight time delay on the fan curve, both for spinning up and slowing down. On my daily driver desktop PC, that means a 0.7 sec delay in spinning up and a 1.0 sec delay in spinning down the fans mounted on the CPU's AIO radiator. These are the maximum delays this particular motherboard allows (MSI MPG B550-I Gaming Wifi). This means that momentary power spikes in CPU usage won't correspond to instant fan speed increases. This means fewer and more gradual fan speed changes and thus less fan noise distractions. The CPU itself has access to plenty of cooling capacity via the radiator's coolant flow.
@More Sly:
Look at this example with the three graphs of CPU PPT, CPU temperature, and CPU radiator fan rpm:
The green arrow shows a momentary power spike with a less sharp jump in temperature. The fan speed shows no corresponding movement.
Another key thing I do is to set the bottom fan curve temperature several degrees Celsius higher than the CPU's resting/idle temperature. That way if there's a slight temperature increase from light usage I won't hear the fans immediately spin up.
The ultimate way of course to smooth CPU fan(s) as possible is to use a water cooler (AIO or custom), as long as it can be set (its fans) to track water temp and not the CPU temp.
Water temp spikes a lot less during CPU temp spikes.
With my custom cooling loop, I set the delay for the CPU radiator fans to 5.0 sec both for spinning up and slowing down; this motherboard (see System Specs) allows for longer fan delays. For my GPU, I have an inline sensor that measures fluid temperature of the exhaust coolant right before it enters the 360mm radiator. This fan curve has zero delay because the coolant temperature fluctuates very little and very slowly. There's no reason to moderate or delay the fan speed here. If the coolant temperature goes up, that's because a large amount of heat is being dumped into the loop.
Noise comes in different forms. Everyone's hearing is different so what might bother one person might be acceptable to another. It isn't just amplitude (volume, like decibels) but there's also frequency. For me, I find fan speed change noises to be particularly irritating so I'd rather have most constant noise with less frequent changes. This is one of the factors that influences how I set fan curves.
I got the Y-cables I needed today and installed them - it's more in the temperature area I'd expect with all five of my case fans running again. ~10-15 °C difference across the board with as much as 20 °C difference at peaks. I was expecting something like ~5 °C, so that's a nice learning experience about just how much having a full suite of case fans really does.
I'm now ~ 35 °C idle and mid-40s on a light load. My peaks are also much, much lower at around 60 °C. Massive improvement more in line with what I'd expect from browsing and videos, etc. Downloads and installs are now at a much more expected high-40s to low-50s.
These numbers are much better.
I have a temporary build with a 5800X in a very well-ventilated case (Lian Li Lancool II Mesh Performance) cooled by an Arctic Liquid Freezer II 360mm radiator. The CPU idles at 30 °C and maxes out at 52 °C with this over-specced AIO.
Having enough case cooling is particularly important for CPU air cooled builds otherwise you're just blowing hot air around the interior of the case.
In my aforementioned build the 360mm radiator is mounted as a front panel intake so I still need good ventilation to move any heat outside the case (top and back exhaust). I used to have the 5800X cooled by a smaller top mounted 240mm radiator exhausting up and out and the temperatures were still pretty good.
