I have 4 WD Elements (external) drives.
2 x 1TB EADS
1 x 1TB EAVS
1 x 650Gb AAKS
I've been plagued by this noise since DAY 1:
1) It happens when the drives are IDLE and not necessarily connected to any host (discard ALL OS related issues).
2) It STOPS as soon as the drive is accessed OR put in Standby (ex: with WD Spindown Utility).
3) It seems to affect the MORE EMPTY drives more often!!
1) Some or ALL WD drives use PWL
2) Preemptive Wear Leveling (PWL) The drive arm frequently sweeps across the disk to reduce uneven wear on the drive surface common to audio video streaming applications. WD AV SATA and PATA drives are ideal for PVR/DVR, DVD recorders, surveillance video recorders, and other video streaming applications (see: http://products.wdc.com/library/flyer/eng/2278-701024.pdf)
3) WD states that WD AV drives are "GREEN drives"... need to say more?
1) PWL is a firmware supported feature that kicks in when the drive is not BUSY (idle)
2) The fact that the noise if much more noticed on drives that are not full complies with PWL "Static wear leveling" mode (see: wikipedia's Wear leveling)
3) ALL WD drives have PWL to protect our data, because there should be NO REASON to remove this feature (it will increase the reliability of the drives, thus, increasing WD reputation)
4) THE ONLY reason WD does not come public with this is because they announce it to be a feature available to specific drives. Is it??? I don't think so. (need to point everyday examples of firmware functionality that gets removed or disabled on capable but "cheaper to the consumer" hardware??? It's only logic!)
Bottom Line: I'm convinced that this is a FRIENDLY healthy noise. NOW... should we start worrying if the noise goes away??? :-))