Dell latitude D630 HDD never spin down!!!

Hi, i have  latitude D630 with the last bios A19 and HDD( WD caviar blue). Recently i start to use the battery more often, is in good condition it can last 2+ hours and i see that the hard drive never spin down for more power save. Even in my old inspiron 1100 (runing windows 7 32bit) the HDD spin down after the time i set in windows. I have try to change the hdd with one hitachi and the same problem. plz someone help me.. :-)