Comment by justsomehnguy

As someone with a bit of experience on this topic:

HDDs doesn't like micromovements. If you put it on a pink foam mat (both a computer and yoga ones) it wouldn't matter. If you 'rigid mount' it but your screws would came lose then your HDD wouldn't like it because it wo&ld result in microvibrations from the self induced oscillations.

Rubber washers are good because they eat those microvibrations. The hard foam which is talked about in the linked article is not good because it is bad from the all aspects - too hard to eat up microvibrations, too soft to be a rigid mount.

The worst thing you can do is to rigid mount an HDD to a case which is a subject to a constant vibration load eg from a heavy duty fan or some engine.