How does your HD sound?

[Hibster_2000]

That could also be down to a lack of mechanical noise at the source.

[NRG]

If you are running say a laptop directly into a DAC then I can believe it makes a difference. I did some tests years ago looking at how the USB power supply was modulated when the HDD was performing head seeks and ways to eliminate that modulation. The only way was to separate the 5v line completely. As for a NAS I’m highly sceptical especially if there is no ground connection between end points.