I have a Z3100, and the fan is nearly always on. One drawback of always being on is the fan gets dirty. Not just in the fan blades, but inside the motor. If it gets dirty enough, the fan can make a noise. Like a Rrrr Rrrr sound. It can also cause the power supply to overheat and produce an error message on the front panel LCD display requiring a poweroff-restart. That happened to me. So I opened up the printer and removed the power supply and lubricated the fan pole.
It lasted six months before it started doing the same thing. My room gets dusty, so - it just seems to suck it all in the power supply.
It took me an hour or two the first time, to open up the printer, lubricate the fan, and put it all back together.
I should like to find a hermetically sealed fan so I can avoid opening the printer a third time, because my fan occasionally starts acting up again.
I've been putting it off. I'm a great procrastinator.