Alrighty! A question I can *really* help with.
Noise:
Those fans will work fine. Depending on how you are mounting them, use either some rubber washers or cut up an old foamy mousepad to isolate vibration, which will obviously reduce noise.
If you use a guard on the fan, make sure it doesn't have a lot of tiny openings since those will induce turbulence and noise.
Voltage:
DC motors are an interesting thing, especially the ones in your fans. They require significantly more voltage and current to start up than they do to maintain speed once running. The point of this is that you can save some power and noise by running them at less than their 12v rating, and you can also overdrive them if you need more cooling.
I'd start by trying them at around 9v. They'll need about that much to spin up, and then would probably be able to continue spinning and flowing good down to around 6v. There are circuits that can be built to do this for you, but I suspect that's more trouble than you want to go through.
Also, I wouldn't use an adjustable power supply wallwart if you have other places it can be used. Instead, I would find an unused 9 or 10v fixed voltage one out of the junk drawer/basement/attic and use that instead.
Hth!
Dan
