If you are into electronics you probably know this very popular digital oscilloscope for amateurs. You might hear about its very annoying affliction: noisy stock fan. You need 5 euro and 20 minutes to make this device virtually soundless.
Since you have to open the box, modification voids your warranty! Be warned. I did not care since I have imported this device directly from Hong Kong two times cheaper comparing to local reseller, and immediately hacked it, making 50MHz DSO working at speed of 100MHz as if it was DS1102E (which made total costs even lower). Anyway, I prefer listening to music instead of spinning fan, so I decided simply replace the fan.
Some people consider airflow distribution, temperature stability, etc. or they mount 80x80mm fan in place of original 60x60mm and so on. My view was much simpler: if I can provide a fan, same size, same airflow efficiency, but more quiet, then I am done. And I did it this way.
I bought already tested fan – Silentium PC Zephyr 60 – for 4 euro, plus 1 euro for shipment. I use Zephyrs in my PC and they work well for over than one year. This model fluid dynamic bearing suspension, makes 17,9 dB of noise at speed of 2500rpm pumping 19,8 CFM (33,66 m3/h). Silicon spacers make it even more quiet.
I think most tough part was opening the box without scratches or any other damages. As always, it is quite simple if you did it at least once :] The photo-story below should make it really easy.
Note: review comments below to see alternate approaches in case opening!