You could always slow the fan down by putting a resistor in line to limit the current. I know someone else here has done this with success. I've got a thermistor and a multiturn pot in mine in an attempt to make it vary speed with temperature but it doesn't work too well. There's not enough change in resistance over the temp range for it alter the speed much (if any!). At least I can adjust the speed to a reasonably inaudible level by adjusting the pot. I think I've designed a circuit that will work, I've just got to get the components for it and try it. I'm certainly no expert in electronics so it probably won't work. Perhaps someone on the board with better electronic design skills could come up with a design that would.