Interestingly Supermicro has a line of, in their words, super-quiet fans they produced for their workstations. Not quite noctua, but better than most. You can

Interestingly Supermicro has a line of, in their words, super-quiet fans they produced for their workstations. Not quite noctua, but better than most. You can take those same Sanyo fans in their plastic quick connect green cowlings and put them in an 847 rackmount chassis. They are a drop in replacement. And if you get the 1250 platinum PSU, those fans run far quieter than their silver & gold line. I've got a water cooled 847 4U server with a small rack of 847 4U 45 drive disc expanders and it is a constant background hum, rather than a small jet aircraft taxiing around the room when using the stock fans.