I'd like to share some experience with about 640 GB Caviar Blue I own.
I've bought a WD6400AAKS-00A7B0 based on SPCR review and other reviews greatly approving this drive for both its perfomance and low noise.
I have been fairly pleased, until I bought another one (based on my good experience with the first one).
Today I've got my first 640GB replaced in advance by WD: new drive is another "B2".
The first one I've got carry the revision -00A7B0
and was made in Malaysia.
Both new drives carry the new revision number -00A7B2
and are made in Maylasia, and made in Thailand for the replacement by WD.
In this order on above pictures.
This drive confirms the review.
It is close to silent.
Seeks are almost inaudible, sounding muffled.
Case closed it's discreet if not unnoticeable.
I've had only one but now it's broken, on its way back to WD...
Visually identical to "B0", only PCB differs, upper casing is engraved P20
Compared with the abovementioned, idle noise seems louder, same motor hum but with higher pitched added noise.
Seeks are rather sharp and "clicky" sounding much metallic and intrusive.
I can hear it clearly case closed.
This drive carries a different motor (same as pictured in review?) and vibrates a lot, much much than other ones.
Bottom casing shows also minor difference. Same PCB as "B2". same upper casing as "B0" (engraved A1
Once suspended, idle noise seems on par with "B2" from Malaysia.
Seeks are sharper than "B0" but not "clicky" sounding as previous "B2".
Case closed it's still audible but discreet.
I'm much happier with this "B2" but still regretting the pleasant "B0".
All impressions given drives hold in hand and elastic-suspended in case.
Based on only 3 samples I own, -00A7B2 drives cannot be directly compared to -00A7B0, each drive exhibiting different noise character.
Upper casing *can* be a clue.
Manufacturing plant *can* be a clue?
I've found the "B2" immediately noisier than the first WD6400AAKS I've had, making me regret it, and that's the purpose of this post!
Perhaps I've got two lemons!
Hope this helps!
Post edited according to MikeC Comment!
Some details added, impressions, pictures and numbers...