Loud as in the fans are spinning quickly, as they do at start up? Or loud as in it is making a bad noise now?
Fans do go bad over time and bearings can make a lot of racket when the fan is near the end of its life. Dusting it off like that can over-spin the fans, not usually a big deal. Could just need more dusting to balance the fans back out, best to turn the system off and clean the fans with physical wiping (I use Q-tips / Cotton swabs)
If they are just spinning really fast for no reason, I would check temperatures. You might have dislodged the CPU cooler or something. Check all of the fan wires, make sure they are firmly inserted into the board, a missing RPM sensor wire might drive them to full speed. Depends on the system in...