Hdd buzzing noise and then pc sound

dramatization: enters buzz buzz buzz buzz buzz …{silet for a second} and i hear it the pc like a normal usb but  i cant see it  on my computer not even in partitions i have valuable data in this hdd and I need help with this please its a green caviar f 1.5 terbytes

Hello,

Test your drive with the Western Digital DLG application available for download at the WD website.

http://support.wdc.com/product/download.asp?groupid=702&sid=3&lang=en