I recently installed a WD Green drive for backups and noticed my case has since given off an audible humm. After removing or powering off parts one-by-one, I've realized it's the new WD Green that's causing it. Compared to my WD Raptor and 500 GB Blue drives, I can feel the Green vibrating when I place my hand on it; it also gives off a high pitched whine. Both are very subtle, but noticeable. Is this normal for Greens?