OK, this is for true DIYers only. Don't blame me if you ruin your $50 Verax fan :)
A user named 'Jshell32' in a Finnish DIY forum Muropaketti has written a short article in Finnish on how to make your fans more efficient and less noisy:
http://murobbs.muropaketti.com/thread.j ... ead=229071
To summarise the main points quickly in English:
1. Remove the sticker/label and open the fan from the center carefully in order not to lose any parts
2. When you have the motor out and the motor casing exposed you will notice that almost all casing have plasting molding residue sticking from everywhere. Scrape or sandpaper it away. Same goes for the 3 or 4 supports that hold the motor in place (don't sand them away, but clean them).
3. Fan blades are unoptimal where they cut air (near the center of the rotor) and where the airflow leaves the blades (at the tip). Sandpaper or otherwise work them to be more even and the edges sharper. Pay special attention to the start of the blades near the center of the rotor on Papst. It's way too thick, so you can make it thinner.
4. If you want, you can add oil or vaseline into the motor itself. I'm no expert in what kind of oil / grease / vaseline to add, if any. Somebody chime in, if they know better.
Now put it all back together. Don't be surprised if you hear a new kind of sound that wasn't there before. It's probably due to the fact that the fan is now spinning a little faster. Most other noises have diminished in all likelihood. You can now lower the voltage a little more and get even more silent fan with same rotational speed.
I haven't done this myself (yet) as I have order of magnitude bigger gains to be made elsewhere still. But it's on my TODO list.
If somebody else tries this, please post your results.