It just so happens that I picked up a Samsung 1-platter 40GB "slim" hdd today -- model SP0411N
. It has slightly better noise specs than the SP1604N
I reviewed (vs. the Hitachi 180GXP and Seagate B-IV 40G): 2.6 bel idle / 2.7 bel seek. The 1604N is rated 0.1 bel higher in both modes.
I can shed no light on why the 1-platter 80G models SP0802N, SP0812N, and SP0812C all have the same noise rating as the 1604N. That the 2-platter 120G models are the same is expected.
I am actually getting delivery of some SP0802N in the next couple of days and will comment on them shortly. In the meanwhile, I did a quick check on idle noise among the 40G and 160G Samsungs and the B-IV 40G. (new Samsung 40G HDD unformatted)
The 160G Samsung is definitely the loudest. It could be 1~2 dBA louder than the 40G at very close range (1cm) according to this SLM. This is not the right way to measure, but there is too much ambient noise right now to be able to pick up on the <20 dBA/1m noise level of these drives.
To my ears, there is a somewhat different sonic character amongs all three drives. The 160G has more of a pink noise "shhhhh" aspect than the others. The Seagate is still a bit quieter than the 40G Samsung. The measured difference at 1cm is 1~2 dBA. Again, very untrustworthy. The noise from the Seagate has less "shhhhh" -- higher frequencies seem more damped; my guess is that this advantage is probably lost once the drives are enclosed in a case.
All three are pretty quiet, and judging from my "buzzing loose on counter" test, have similarly low vibration.