If the amp is on the other side of the room, with the silent fan replacement, then it is unlikely you could hear anything whatsoever. If the amp is sitting right next to you, it is probable you would hear it. With the stock fan, it's easy to hear from the other side of a 20' room. Replacing the fan costs about $8 plus shipping of the fan, and it takes about 20 minutes do the modification. You remove the amplifier cover, then remove the stock fan and shroud, and screw in the new fan. The fan is connected to the circuit board with a little plug like the ones you find in computers. The replacement fan will not have a plug; so you can either cut the wires to the old fan and use that plug or scavenge a plug connector out of an old computer.
-Chris