All new Reds in sale are now the louder ones. I'm not sure if the difference begins with NasWare 2.0 vs NasWare. I think they did it to increase performance (they must internally disable Automatic Acoustic Management). By HDTune, average seek is better now - 16 vs 21 ms, but hell they are so loud now, if you have Nas at home, especially fanless Nas like the Qnap's one, you will hear the difference.
As I found, all of them performing Background Media Scan on idle every 10 seconds, that is fine, but only on old Reds you can't hear it (as you can't hear seeking).
I tested 4TB made on february 2014 (I have no model number because I returned it), 3TB made also on 02/2014 has model WD30EFRX-68EUZN0. As I checked web about 4TB, they should be loud from beginning (25/28 dBA).
I found WD made at least one thing "quiet" - they changed pdf datasheets on their web site, without a notice. Here is current datasheet compared to 2013 one, what I downloaded via archive.org:
I think your review should be updated, because now everywhere are reviewed older Reds, and people buying them when they need quiet Nas.
I'm really surprised there is less talk about this here. I mean it looks like there was a major change in the noise level of one of the top ranked drives on this site and even the (outdated?) reviews don't contain a warning?