I found that putting them on something soft helps a lot. It seems to be mostly vibrations that are transferred to whatever it's sitting on.

Try styrofoam, a couple layers of soft packaging wrap, thick cloth, etc.

My other hack is WOL + auto-suspend for my NAS. Wakes up for backup jobs, goes back to sleep when done (and there are no SSH sessions left open). Very hacky but works flawlessly. (Usually.)