I have RMA'd a WD drive, it was easy. They even send you a new drive, and let you ship back the old one. Pretty cool, in my opinion. Gives you a chance to duplicate the drive, wipe the one you're sending to them, and ship it out.
Regardless of what action you choose(buying a new drive, having the one you are using now RMA'd, etc.), you need to back up the drive NOW. They have a bad habit of making noise right before they crap out.