I have mostly been reading and asking questions so far, so I think it's time to contribute something back.
I'll start off by listing the least noisy modern dvd-rom and cdrw drives I've been able to find personally. My search has not been exhaustive, but I have tried several models from LG, Samsung, Plextor, Toshiba, Pioneer, Sony, LiteOn and Yamaha.
I've also read all dvd-rom and cdrw reviews on the net (that I could find), which also touch the acoustic performance of various drives.
DVD-ROM drive (least noisiest at default setting)
1. Sony DDU1621 16x DVD-ROM (manufactured by BTC?)
+ This drive is not only the least noisiest (a lot less vibrational
noise and swooshing noise than LiteOn, Samsung, Toshiba or Pioneer 16x models)
- It has no error correction for dvd-discs. This is a major bummer and as such, makes it a bad choice for a HTPC main drive
+ It has decent DAE speed, ok level C2 accuracy (not among the best) and superior error concealment to anything I've found yet (good for ripping scratched CDs)
- Of course, it is not silent, but much easier to make less noisy than any other modern (16x) dvd-rom drive I've been able to find
- If you can find older 4x or 8x drives, you may get even less noisy drive
Least noisy modern CDRW drive
1. LG 4480B 48xcr 24xcrw 16xdvd-rom (combo unit)
+/- It's not silent, but subjectively clearly lot less noisy than any 48x (or faster) LiteOn model
+ Firmware revision 1.0 caps DAE at 40x sligthly reducing noise (of course one can use drive speed to further cut down on noise)
+ Has excellent scratched disc reading performance
+ Burn quality is very good on TDK, Acer, Mitsubishi and TY media (48x certified) I've tried
- Again, an older 4x or even 12x drive can performe much more quietly
I'll be experimenting with further noise damping when I get some silical gel mats or other padding material to put between the drives and the case.
If you have better suggestions for a modern/fast/reliable drives that are not extremely noisy, please pass them on.