The fan is probably mechanically made to have minimum spinning speed at 55%. I doubt you can do much except if you are really bothered, you could remove it and since GT 640 is a very low power card, passive cooling might be enough.
I believe it's a software problem not a hardware problem; before I installed the Nvidia drivers the fan was running almost silently but you could still hear it. If there's not a way to change it in the software, what would be some other suggestions?
I know for my CPU cooler (Noctua nh-l12) you can add an adapter wire to the fan that will slow down the fan speed. Is there an adapter I can get for my GPU fan to fix this?
Or could anyone recommend an aftermarket GPU cooler that is less than 7" and is single slot?
EDIT: thanks for the suggestilon, I'll try updating the BIOS and see if that heps. Would you mind giving me a link? I can't find anything official from Galaxy or Nvidia, just some 3rd party links.