I agree with Adzsask in getting your data backed up.
TBH, I think what you're hearing are just seek noises (light grinding/creaking kind of noise...sorry, it's hard to describe the sound) which are normal. If your concerned, you can submit it for RMA if it's under warranty. I recently sent back a WD RE3 for RMA and they were great to deal with...no hassle and the entire process took just over a week.