most silent way to vent? pls help

I have a small box 2ftx2ftx4ft and i plan to use it for scrog growing. I have a 150w hps and carbor filter. I now need to as silently as possibly vent the heat.. Any good advice will be greatly received...

I bought a 4" 170 cfm inline fan for $80 with a fan controller and hooked it up to my filter. Thing is silent and keeps my temp at whatever the ambient temp is surrounding my cabinet. Heres a link to my box

https://www.rollitup.org/general-marijuana-growing/379500-check-out-my-box.html

and where I bought the inline fan

http://htgsupply.com/viewproduct.asp?productID=52557