Those were pure-bred datacenter servers, noise was completely irrelevant.
The fans are temperature controlled, but even on lowest settings they are quite loud.
You can replace the fans with some lower-rpm ones. IIRC the minimum threshold is somewhere around ~6000rpm for the system fans. They will throttle to lower rpms, but they must spin above that threshold during startup.
For the PSU the threshold is much higher (>10k rpm), and the ALOM will shut down the system if the threshold is undershot. There's only an "OK/FAIL" value for the PSU fans, so I tested that with a function generator (and a lot of cold boots, because the FAIL status won't be reset by the initial system check).
I've used a simple adjustable frequency generator (a few bucks on aliexpress) to fake the rpm signal with a 30kHz GND signal. Minimum threshold is somewhere around 24kHz. (IIRC this corresponds to 12k rpm)
I've replaced the Fans in my T1000 with Sunon MB40201V1 (7200rmp, 0.84W, 0.25m^3/min). They will run at ~4500-5000rpm under normal load, except the PSU fan which always runs at full speed and it definitely has to as the PSU gets quite warm/hot! It never triggered the overtemp, but still it's really at the edge of my personal comfort zone - it gets too hot to touch if the system gets some load.
With those Sunon fans the system is much quieter and bearable, but still, this is a 1U server and was never designed to be quiet. So there's no chance in hell you will get that system quiet enough to be running unnoticed in your living room. There's still a very notable airflow noise and I wouldn't try to go lower with the fans. As said - the PSU already gets relatively hot despite the room being air conditioned to ~22°C.
And no - noctua fan's won't work. They are only quiet because they don't move any air as soon as there is the tiniest bit of backpressure, and you *will* need fans that can build up some static pressure in a 1U system.
Here's the 'showenv' output after a few minutes of uptime (running OpenBSD in primary LDOM and in 2 LDOMs as redundant firewalls)
Code:
=============== Environmental Status ===============
--------------------------------------------------------------------------------
System Temperatures (Temperatures in Celsius):
--------------------------------------------------------------------------------
Sensor Status Temp LowHard LowSoft LowWarn HighWarn HighSoft HighHard
--------------------------------------------------------------------------------
MB/T_AMB OK 31 -10 -5 0 45 50 55
MB/CMP0/T_TCORE OK 49 -10 -5 0 85 90 95
MB/CMP0/T_BCORE OK 49 -10 -5 0 85 90 95
MB/IOB/T_CORE OK 55 -10 -5 0 95 100 105
--------------------------------------------------------
System Indicator Status:
--------------------------------------------------------
SYS/LOCATE SYS/SERVICE SYS/ACT
OFF OFF ON
--------------------------------------------------------
----------------------------------------------------------
Fans (Speeds Revolution Per Minute):
----------------------------------------------------------
Sensor Status Speed Warn Low
----------------------------------------------------------
FT0/F0 OK 4435 2240 1920
FT0/F1 OK 4342 2240 1920
FT0/F2 OK 4483 2240 1920
FT0/F3 OK 4296 2240 1920
--------------------------------------------------------------------------------
Voltage sensors (in Volts):
--------------------------------------------------------------------------------
Sensor Status Voltage LowSoft LowWarn HighWarn HighSoft
--------------------------------------------------------------------------------
MB/V_VCORE OK 1.31 1.20 1.24 1.36 1.39
MB/V_VMEM OK 1.79 1.69 1.72 1.87 1.90
MB/V_VTT OK 0.87 0.84 0.86 0.93 0.95
MB/V_+1V2 OK 1.18 1.09 1.11 1.28 1.30
MB/V_+1V5 OK 1.48 1.36 1.39 1.60 1.63
MB/V_+2V5 OK 2.47 2.27 2.32 2.67 2.72
MB/V_+3V3 OK 3.27 3.06 3.10 3.49 3.53
MB/V_+5V OK 4.99 4.55 4.65 5.35 5.45
MB/V_+12V OK 12.25 10.92 11.16 12.84 13.08
MB/V_+3V3STBY OK 3.29 3.16 3.23 3.43 3.49
-----------------------------------------------------------
System Load (in amps):
-----------------------------------------------------------
Sensor Status Load Warn Shutdown
-----------------------------------------------------------
MB/I_VCORE OK 20.560 80.000 88.000
MB/I_VMEM OK 5.820 60.000 66.000
-----------------------------------------------------------
----------------------
Current sensors:
----------------------
Sensor Status
----------------------
MB/BAT/V_BAT OK
------------------------------------------------------------------------------
Power Supplies:
------------------------------------------------------------------------------
Supply Status Underspeed Overtemp Overvolt Undervolt Overcurrent
------------------------------------------------------------------------------
PS0 OK OFF OFF OFF OFF OFF