Thanks, applying pressure to the top of the NAS turned out to be very helpful! I stacked a pile of my heaviest books on it, and while It is still louder than I hoped for, it is definitely less noise than before.
>Yes, more mass is often helpful
And are you saying that Blu Tack on the feet may reduce the noise as well?
>Yes, could help a lot. depending on the surface that its sitting on.
Upping the fan speed really seems like a last resort, but since the fan definitely does not disturb me it might be something to try. But would that not make the NAS go into a more demanding state overall, potentially upping the noise from the HDDs?
>this suggestion is not fluff, acceptable sounds to mask objectionable sounds is a widely used strategy. There is no danger of a "more demanding state" or chance of "upping noise from the HDDs" turning up the fans merely means that they will see their source power a higher % of the time and that will cause them to spin faster, increasing their cooling and with a side effect of creating more fan noise.
EDIT: I found this about applying velcro to the disc slide: https://www.reddit.com/r/synology/comme ... _solution/
Seems like something like this is what your are suggesting.
>Yes something like that. a barrier between the two hard surfaces that are now oscillating against each other.