Old HP T&M equipment can be quite loud
I exchanged all my fan's with Noctua models
Though your model is a 115VAC type, I guess that you can find a low aux. voltage in your supply - like 12 volt
The AC types consumes quite a bit of power
(not exact your model)
http://www.comairrotron.com/content/sprite-ac-su2b1-19028268aBut look for a Noctua NF-A8 FLX
If the power supply's aux. voltage is to high, either use the supplied "Low Noise" adapter or build a small power supply with LM7812 or LM317
In my HP E3634A I build a small regulator with a thermistor, so it is very low noise at light load
At max load the thermistor senses the heat sink temperature an adjust acordingly
Enjoy your silent power supply