Western Digital Caviar Green (WD10EADS) Failure

On my desktop PC I have a 1 TB secondary drive which I use for storing photos, videos, music, and etc.  I was using a WD Caviar Green model WD10EADS, and it developed a strange behavior.  File access slowed to a crawl, with wait times of between 3 and 5 seconds to read from or write to a file.  Disk utilization (resource monitor) showd 100%, but the drive wasn't making much noise.  According to the SMART check, everything was still within spec.  Then I tried to do a sector test on it, using WD's Data Lifeguard tool, and it failed about 2/3 the way through, "Error 8: too many bad sectors".  

My theory about what is going on is that the drive controller, for some reason, is not able to "wake up" anymore, and so sometimes when you ask for a file it takes a long time to actually read it or write it, but my data did not appear to be damaged--I was able to copy everything off of the drive, it just took multiple tries for some files.

Thanks to a 3 year warranty, I am able to send the drive back for replacement to Western Digital.   I'm a little spooked by the failure though, and I am going to replace the drive with a non-Green model for now.  I liked how quiet the Caviar Green was, but it wasn't the fastest drive even when it was working.