Make sure the drive isn't being used, and then run the WD diagnostic tool on them:
WD Support / Downloads / SATA & SAS / WD Caviar Green / GP
If the tool generates any error message, copy-paste the error message (a code of some sort) into WD's RMA form to begin the RMA process. If there's no errors, then I'd just continue using the drives - depending on how you filled up the drive or what you're doing, you'll get different seeking sounds from them.
You
always want backup copies of any data you don't want to miss. It prevents the

from you and the

from many forum-goers here due to the posting "I lost my data" type thread. Don't forget how software, weather, and other living entities can take out storage devices.