I did some recording of all the fans this evening and converted the wav files to mp3, but I don't know how I will post them here since I have no space to upload the files to. I'm asking a buddy of mine if he can host them.
I also tested all the fans with running at low voltages and all the fans except the Sunon screamer would actually start and run with a little less than 5 volts fed to them. None of motors on them got particularly noisy either. And using the included speed reducing adapters the Noctua got almost silent and the Zalman got pretty darn quiet.
Here is the way I would rate the noise from the fans, from quietest to noisiest:
1. Noctua NF-P12 - quiet
2. Scythe SY1225SL12M Slipstream - quiet
3. Yate Loon D12SM - not quite as quiet, tied with S-Flex
3. Scythe SFF21F - S-Flex not quite as quiet, tied with Yate Loon
5. Zalman ZM-F3 - just a hair noisier than the YL/S-Flex, primarily higher pitch
6. Panaflo L1BX - just a hair noiser than the Zalman, primarily higher pitch.
7. Panaflo M1BX - moderately, more airlfow noise and higher pitch than L1BX
8. Delta EFB1212LE - moderately noisy, much lower pitch than all other fans, but definte blade popping noise.
9. Sunon KD1212PMB1-6A - very noisy, both in pitch and motor whine. Moves a crapload of air.