I have a 24V 172mm fan. It's stall voltage is around 6V. This means it runs fine off a 12V supply from your comp. As for silent, sadly not. Bearing noise alone makes it non silent, at 7V it's a low rumble, at 12v it's a quiet roar, at 24 it's a loud roar.

As the saying goes - the only silent fan is one that's switched off.