Besides skipping the fan altogether, you can also run a fan on less than its original full power. That way it can be very quiet, and still move some air (and probably last longer). A bit of airflow is a lot better than none. To reduce the power, I've used the following methods:
Small 115-120VAC fans: put a capacitor in series, about 1 uF, experiment to find the right size. Must be a high-voltage (400V, better 600V) non-electrolytic capacitor. (If the capacitor fails (shorts out due to a power spike) the fan will go to full power but nothing else bad will happen.)
Small 115-120VAC fans: replace with a 230VAC fan of same physical size. It'll usually run on 115VAC, but slowly and quietly. I've found some 230VAC fans at "All Electronics", but they run VERY slowly on 115VAC, perhaps too slow to bother.
Small DC fans: put a resistor in series. E.g., for a 12VDC 0.1A fan, that's a 120 ohm load (12 / 0.1), put something of same order of magnitude in series, e.g. 50 ohms (1 watt - put the resistor in the airfow area, that'll keep it cool).
Small 12VDC fans: replace with a 24VDC fan of same physical size. It'll usually run on 12VDC, but slowly and quietly. I've found some 24VDC fans at "All Electronics" and they run usefully fast down to about 6VDC!