Let me do some speculations on the given indicatives in this picture. According to the sticker on the very front-left of the cover, the way the “Intel Xeon inside”-Label is pinned and the apperance of the drive caddys i very much guess that this is a HP Proliant Gen8 Server. Am I correct?
If so… welcome to the club of users experiencing some strange fan speed behavior. This is a well known bug with these mashines. I also have trouble with these and never got them lower than 30% fan speed (while the machine is literally doing nothing).
I managed to lower fan speed from about 40% to a little less than 30%. If you have a “HP Ethernet 1Gb 4-port 331FLR Adapter” installed it is propably connected to the 16x PCI-Slot. Put it into the 8x PCI-Slot (on the opposite side of the board) and downgrade it’s firmware to 17.x.x. (from 20.x.x). As I said… that saved me 10% fan speed which is not really satisfying.