I have recently bought the papst 412FH fan 40x40x10 mm 12Vdc ( http://www.papst.de/pdf_dat_e/S11gb.pdf )
I've no idea what the noise is that it make's but I can't here it when it's in the car and I when the Empeg is on the table there is some noise but that doesn't bother me. (The data sheet states it make's 29dB(A) )
They now also have an online shop but I don't know if it's world wide....
For the people in the Netherland check out www.alternate.nl they sell them for EUR 14,-
Other country's may have an own alternate website/shop, germany for instance.

Greetings, Robert