well which miner? s-1's or other types of miners.
If you want to make s-1's quieter it can be done a few ways.
It's a Dragon 1 Ths but applies to Avalon 2 miners too.
Anybody changed their fans?
The problem is that any fan that pushes 100CFM of air is going to make a lot of noise just moving the air around, and if there are metal parts in front of or behind the aiflow then the air is going to make noise moving over those parts (grills, heatsinks etc)
You can't make these things "silent" without using slower fans which will make them overheat.
All you can do is maybe get a different type of fan whine noise (higher or lower pitch) that will help lower the decibels by a few percent which may or may not make it bearable.
What you want is high CFM fans, that have good static pressure, very similar to what you want attached to a heatsink on a cpu cooler or on radiators if water cooling. Add to the fact that they often need to be PWM fans (4 pin) so their speed can be controlled and there isn't alot of choice out there.
Here are a couple of 120mm fans that I would reccomend, but as I said personal preference may play a part in the "type" of sound that you would consider annoying.
Coolermaster JetFlo R4-JFNP-20PK-R1 (Dark, No LED)Fan Speed 800-2000 RPM (PWM) ± 10%; w/ silent adapter: 1600/1200 RPM (fixed)
Air Flow 95 CFM ± 10%
Air Pressure 2.72 mmH2O ± 10%
Life Expectancy 160,000 hrs
Noise Level 19 dBA (1200 RPM with included silent mode adapter)
28 dBA (1600 RPM with included silent mode adapter)
12-36 dBA (PWM)
Air Series SP120 High Performance Edition High Static Pressure 120mm Fan CO-9050007-WWAirflow 62.74 CFM
Static Pressure 3.1 mm/H20
Sound Level 35 dBA
Speed 2350 RPM
Scythe Grand Flex PWM SM1225GF12SH-PFan Speed: 600 ± 250 rpm ~ 2.400 rpm ± 10%
Noise Level: 13,5 ~ 39,5 dBA
Air Flow: 24,2 ~ 96,8 CFM / 41,1 ~ 164,4 m³/h
Static Pressure: 0,28 ~ 4,55 mmH²O / 2,75 ~ 44,62 Pa
Then there are 38mm fans which are all similar to the ones already installed in many mining machines.