if this noise problem is something new your fan may have a problem with it,
if you need to replace it they also sell stealth fans online
The Phresh HyperFan Stealth delivers the highest CFM's per watt of any silenced fan in the industry. Comes with a speed controller and integrated mounting brackets.
Combining the original hyper fan with the silencing canister technology you get the Phresh HyperFan Stealth series this results in a reduction of 15 dba's perceived to the human ear as 75% quieter perfect for your grow rooms and grow tents.
Like the original hyper fan this uses 50% less power than traditional fans.
Thanks, I am about to order a fan, and had settled for a soler&Palau TD350/125, but then I saw your post and thought this needs to checked out. Trouble is I can't find any information on the Thresh Hyperfan, except from growshops, and that is mostly hype with no mention anywhere of actual dB(A), power consumption and airflow at what static pressure level. They are not mentioned on the Thresh homepage.....looks like they are not made by the same company that make the Thresh filters........googling "laminar blade design" yields nothing (although it sounds satisfyingly "Hi-Tech"!). Do you have a link to the manufactures website?
Here is the TD350
http://www.solerandpalau.co.uk/docs/catalogo_general/en_757_768_td_silent_fid6771.pdf
As a rule, I always make a 100 % allowance, i.e. double the specs, for what I am looking to achieve. In this case a 10 m3 room with a nominal turn-over of 15 times/h. This in order to compensate for flow resistance from the carbon filter, ducting and bends.
[TABLE="class: tablenumeric, width: 609"]
[h=4]Table 1: Examples of sound pressure levels in relation to hearing threshold and pain threshold (in dB SPL)
The range of human ear’s audible sounds goes from 0 dB SPL (hearing threshold) to 120-140 dB SPL (pain threshold)
[/h][TR]
[TH]Source / observing situation[/TH]
[TH]Typical sound pressure level (dB SPL)[/TH]
[/TR]
[TR]
[TD="align: left"]Hearing threshold[/TD]
[TD="align: right"]0 dB[/TD]
[/TR]
[TR]
[TD="align: left"]Leaves fluttering[/TD]
[TD="align: right"]20 dB[/TD]
[/TR]
[TR]
[TD="align: left"]Whisper in an ear[/TD]
[TD="align: right"]30 dB[/TD]
[/TR]
[TR]
[TD="align: left"]Normal speech conversation for a participant[/TD]
[TD="align: right"]60 dB[/TD]
[/TR]
[TR]
[TD="align: left"]Cars/vehicles for a close observer[/TD]
[TD="align: right"]60-100 dB[/TD]
[/TR]
[TR]
[TD="align: left"]Airplane taking-off for a close observer[/TD]
[TD="align: right"]120 dB[/TD]
[/TR]
[TR]
[TD="align: left"]Pain threshold[/TD]
[TD="align: right"]120-140 dB[/TD]
[/TR]
[/TABLE]
)))
Potential health risks of exposure to noise from personal music players and mobile phones including a music playing function (2008) 
