I installed a WD Scorpio Blue 640GB 5400 RPM drive in my Macbook Pro from 2009 (13"). For some reason, the drive platters are not spinning down and they just keep going. I made sure that "Put Hard Disks to Sleep" in Energy Saver was checked, but it doesn't work. I know that this will contribute to a shorter HDD life span, so how can I fix this? Thanks.