Well, that depends... Hard disks should be more around the mid 30's, and yours is already hot enough to burn you. 4 degrees can be the difference between melting lube or not.
I get that you're probably trying to improve things without unnecessary spending, but I think possibly it would be wise to re-examine your objective. If this machine is near a CNC milling machine, why does it have to be so quiet? If the noise is irritating because the CNC is idle 99% of the time, then shut it down or hibernate it 99% of the time, and extend it's service life.
If that's going to cause more nuisance than the noise, then
spend some money. If this machine is running a piece of business critical equipment,
what's the cost of failure?There are all sorts of options from Noctua fans to large passive heatsinks to liquid cooling to SSD's (cooler than a hard disk) to replacing the PC itself with more modern cool-running cpu/gpu combos... If you only want to look at cooling, then target the NOISIEST fan first. Start here...
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