Here is a simple way to reduce the noise from a hard drive, when used in a desktop case.
Two pieces of foam are simply wrapped around the drive and secured with tie wraps.
A hard drive sounds noisy because the case resonates with the head movement etc.
So decoupling the drive from the case makes things much more peaceful.
If you choose a drive that is already fairly quiet, then mounting like this makes it
really quiet.
An earth wire is attached, because if the drive was screwed to the case it would be earthed.
The drive simply sits on the bottom of the desktop case under the DVD drive.
If you get the amount of foam just right, the drive is a fairly tight fit in the case.
You could attach a PAPST 12 db fan to the drive if you are concerened about heat.
Foam attached to the drive.

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Side view, air gap underneath and Earth wire.

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Acoustic cushioning close up

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Happy tweaking,
Mark G.