Hi there sudhir08,
Sorry that you are facing some issues with your WD drive.
I would suggest you to start with just backing up the most important data stored on the drive.
Have you tried attaching it with different cables(both SATA and power ones) to a different port? In case you haven't, you can try that.
You can test it with WD's DLG tool as well(both short and extended tests):
http://products.wdc.com/support/kb.ashx?id=CS9gma
Is the drive under warranty? In case it is, and the tests fail(or that sound persists even after changing cables and ports), you can contact the place you got the drive from(or contact WD's Support):
http://products.wdc.com/support/kb.ashx?id=AuNqON
Let me know how this goes,
D_Know_WD