I am actually going to play around with programming some financial models in cuda myself, I am not planning to use any of the standard applications at this point.
However, unless you mod the bios (there's a thread about), every 460 is loud, even those MSI (and most of 560, which are usually better at idle, but it's not your case). Take note that we're talking about 24-26dB at load, usually.
Are the newer cards (e.g. Gainward Phantom 560 GTX suggested by lodestar) any better?
One of the best sounding Nvidia I've ever had is the GTS 450 Cyclone OC, but I don't know if it's enough powerful for you (and if there's still available, as it's a almost 1 year old card).
I definitely need to be able to perform double precision calculations. My current 250 GTS (which is horribly loud btw.) was able to do only single precision. I need to check GTS 450.