We have two of the N150 netbooks in the family. While that's a nice and quiet, annoying the other with scratching-scraping read and write operations. As has been shown, a Samsung hard disk is installed in the soft N150, while the other with a Seagate drive (ST9250315AS) is equipped.
Unfortunately, the Seagate drive does not support tools for reducing access noise by AAM feature (Acoustic Management). Corresponding firmware updates for the Momentus 5400.6 series are not going to get from Seagate. Merely turning off the APM features (prevent the permanent parking position of HDD heads) by means of various tools reduces the amount of annoying scratching sound.
My conclusion: The Seagate drive is a real nuisance for those who desire to have a quiet netbook. Because Samsung built several boards at N150, I buy the pig in a poke.