A while ago I lowered the voltage of the fan in my to silence my signal generator. It was better, but over time I still found it rather noisy. So today I came up with a simple solution to silence it some more.
I took a small piece of floorboard insulation. The blue stuff, about 3 mm thick. Then I cut 2 square pieces and cut those diagonally, so I had four triangular ones. From the long side I cut out little squares to make room for the screws. Then I opened up the generator again, loosened the screws of the fan and wriggled the insulation pieces in there, on at every corner. Tightened the screws again and PRESTO: