The hdparm version I gave you, as well as the original version, both treat "0" as "OFF", meaning, "use the drive's default, whatever that is". So the lowest you can go is likely either "1" or "128" (really, try it).

It will only affect seek noise, not rotation speed. So you'll hear a difference, if any, only when the drive is seeking around. On desktop drives, it makes a HUGE difference in grinding levels.

Cheers