I would probably have to say that it is just coincidence that you noticed the fans being louder after the update. It is more likely that since the computer has been on, it has just started to heat up a bit. Do you have a CD running in the drive? What programs are running? If there are quite a few, or if you are running some real proc heavy apps, it may be causing the computer to work harder, thus making the internal components hotter, which in turn would kick the fans up.
It most likely is nothing to worry about, unless it keeps up or gets any worse. You might also want to check to see if there is anything nearby that could be adding to the heat. Try shutting the computer down for a while and see if the fans kick on like that right away when you boot it back up.
