I have a 95W AM3 FX8300 also with stock fan/cooler. I didn't overclock. It is not as quiet as I would like it to be, but most of the time it is fine. Previously, I had 65W C2D E8400 but using the 90W cooler for Prescott CPU, so I manually reduced the fan speed in the BIOS. That motherboard did not have intelligent fan control in the BIOS to vary fan speed based of CPU temperature.

You can check if the motherboard BIOS supports intelligent fan control which will keep the fan speed low when the CPU is idle. Or, manually override the fan speed control in BIOS to force it at the noise level comfortable to you and depend on throttling or thermal-trip to kick in in case of CPU over temperature.

Of course, depending on how you wish to spend extra dollars, you can always buy a better fan/cooler or water cooler kit for CPU.

From my experience, most aftermarket coolers' fans cap at around 1800 rpm which should be quiet enough. The stock cooler can go as far as 6000 rpm which explains why it can be noisy at times. Not sure about what kind of noise, but sometimes fans that have been used for a long time might start with a very loud noise upon cold startup, that would usually go away after a while, and this condition worsens over time, implying you'll have to replace the fan with a new one.

The cooling is usually compensated by heat pipes and relatively larger heatsinks. Not sure about the width of your case (whether it supports full-height PCI/PCIe cards or only half-height ones), you will need to make sure that the heatsink of your cooler isn't too large to fit in the case.

If your case allows, you may consider putting some additional case fans (size depends on your case) to improve the airflow, which can help keeping the system temperature (not only CPU) at an acceptable level.

there is no reasonable way to get the phenom II stock cooler quiet. I have used one temporarily on a 65W dual core Athlon 64 and it was just as obnoxious. If you wan't to make that system quieter you need to get a better cooler.

For the sake of completeness, yes.

Some motherboard allow you to enable or disable cores in the bios, but in my experience this is not a common feature.

You can reliably disable cores in your OS, which I believe just prevents the operating system from recognizing and scheduling threads on those cores.

https://ccm.net/faq/616-multicore-cpu-how-to-disable-a-core

I have a core2duo system I am building for early XP, and my plan is to disable it down to a single core for less fuss with dual core sensitive games.

Just looked up... core parking wasn't implemented until Win7.

If your board / BIOS has a core unlocker, then enabling that feature may allow selection of the available cores - if so, I'd suggests stress testing on all cores with some software HWmonitor, and picking the ones that show the lowest temp

Can't you just decrease Vcore and/or NB Voltage ?

If your BIOS does not have such Core disabling function you can use K10Stat to test Core disabling. It's available at the NB tab of K10Stat. Unfortunately it works only for the next warm reboot so it's not a permanent setting and requires a Windows reboot. The setting also cannot survive suspend/wake up cycles (moreover can results in hangs). But you can use it to test if it has any effects on your thermal/noise problem.
As agent_x007 suggested you can try to under-clock and under-volt your CPU instead. K10Stat is also a perfect tool to create such profiles and start K10Start at every boot to set these profiles. (You should disable Cool & Quiet in your BIOS if you want to use K10Stat instead).
In case of Phenom II disabling cores does not have an enormous effect on power consumption if the additional cores are idle/not used anyway. But under-volting under-clocking can have.
https://sites.google.com/site/k10stat/
For core disabling on WinXP try to use v0.91. Core disabling function of later versions does not work on WinXP.

Fans can be undervolted too, if you're not afraid of rewiring things. Most fans use the 12V, but sometimes they will work on 5V while running slower (quieter), or connect it between 12V and 5V to get 7V.

Its like Phil read my mind 😲 !
https://www.youtube.com/watch?v=auUC9j9fnPY

Albeit the 125W version but talks about disabling cores and undervolting, ridiculous how useful these CPUs are, after 10 years but thats not the purpose of my build.