My rpi has been really loud with its fan for the last long while. I could still hear it behind a cupboard and a door. While diagnosing a usb thumb drive’s i/o issue, I decided to dampen the sound.
Using 6 roofing screws, I pulled the rubber and metal washers off and put on the fan mounts to the case. It has had the effect of increasing the mass of the case and reduced the sound in pitch and volume, I expect the lower pitch will be easier to muffle.
It is much less annoying.
The washers were a bit larger than the fan mount plastic sockets. I did not try to force it to sandwich between the fan and the case.
A Flirc case works well too.
Yes, I could have spent money on the case this late in the game, but I thought 20 mins and some spare washers was easier and I wouldn’t have to think about this project for the next two days.