listen so many people gave you there reply, and here is another , So what are you trying to do ? you want to ISSOLATE THE NOISE, many people here have done so and are telling you to do so, You know there is an actual part that is specificly made to reduce noise and vibration for fans , They are called VIBRATION /NOISE ISOLLATORS, do a serach on them ,I will even bet you the MFG of your fan will most likly have them , they are weight specific to the fan ,So if you buy them make sure you know the weight of your fan. Now if you dont have enough duct work on your fan or ducted incorrectly this Noise can also be your probem, HVAC companys Also MFG a product for that .They are called SOUND TRAPS, do the serch get one that will handle your FANS CFM and all will be good,And No these products wont be carried or proberly known from the guy in hydro/nusery store ,WHY because they No JACK SHIT about moving air ,Just as I know JACK SHIT about growing ,but hey Im tryen to learn , if I can just consentrat on this site with out looking in GROW ROOM Design ,But these questions keep sucking in this retired HVAC GUY.