Hi, ok it's now midnight ish in rural Gloucestershire and I can't really hear any ambient noise. Basically at the moment any noise stands out clearly, no idea what that makes the actual noise level, maybe as low as 10~12dB(A).
I've unplugged the CPU fans and turned the case fans down to zero leaving the 2x 92mm fans on the video card and the 80mm PSU fan, like so:
The WD20EARX is outside the case, under the desk, in a Scythe Quiet Drive.
A Scythe Quiet Drive is, in my opinion, a great bit of kit. Inner aluminium shell around the drive and tightly screwed to it has rubber (like) pads on it the damp it from the outer while still transferring heat top and bottom. All round sides is padded with foam, probably takes 2~4dB(A) off a HDD, that's the difference between a loud and quiet one. Does need a lot of room and not cheap either but will be useful until mechanicals are totally replaced by solid state.
Also comes with rubber blocks to fit it in a 5.25" bay and there is a 2.5" drive version that fits a 3.5" bay so could use a laptop drive and fit in normal desktop drive bay and be pretty quiet.
I cut a hole in case floor behind the motherboard tray...
and put it out the case, sitting on bit soft foam:
From seating position I can't hear it, when I kicked off a search the seeks were faintly audible.
If I put my head in front of the desk, ~0.5m from the drive I can vaguely make out it's noise, with my ear right up to it it's easy to hear.
I then tried again with the drive removed from the SQD. Idle noise was louder, but still quiet and unobtrusive, barely audible from my seating position with the drive under the desk. Forgot to test out seeks...
I then mounted the drive in the case, 4 screws tight in to an aluminium case, not good for noise...
There is nothing between the drive and the outside and idle noise was now quite audible, typical HDD like really, some whoosh and touch of high metallic whine, but bare in mind this is dead quiet environment and PC and the absolute level is quite low.
Seeks were plainly audible, but that's expected when screwed to the case, especially open aluminium one.
To try give an absolute level on this I employed a 1000rpm 120mm Xilence case fan, this is a decent smooth sounding case fan.
Off a Fanmate at full 950rpm, I was sitting in front of the PC, the fan was a touch quieter than the EARX, I lost the sound of the fan ~800rpm.
With the drive off I could make out the fan's noise down to ~600rpm
You can use Crystal Disk Info to read the SMART info and compare to mine:
Example of unhealthy drive:
[This Seagate 5k4 laptop drive is way louder than the rest of my PC!]
If your drive is making unpleasant noises I would suggest that it's not as it should/could be and see if you can RMA it with WD for a replacement.