WD15EADS grinding - hardware or firmware??

I recently bought a WD15EADS 1.5TB 'Green' disk made by Western
Digital.

I plugged it in, on a SATA docking unit that I use.

I did some writing to it. After the write activity stopped, the heads
kept on grinding. Even after I did a soft-disconnect of the drive and
just left it plugged into the dock, the grinding continued.

I did some digging, and found a forum post in which the poster
described similar symptoms, and actually recorded the sound the drive
makes. This is pretty much exactly what I'm hearing:

http://boomboost.com/example/wd15eads_bad.mp3

I don't know whether this is a firmware issue and can perhaps be fixed
with a firmware update (can I even flash the firmware on these
drives??), or if it's a hardware problem requiring an RMA.

Opinions or insights would be appreciated!!

BD