need help sound proofing (noisy fans)

ok, well i am building a grow box in my closet and i have 2 inline 6" can fans... one is for exhaust and the other for my cool tube. both of them are VERY loud, even just one! you can literally hear them from the other side of the house =/
is there anything i can do to quiet it down? fans are well insulated where mounted.
can i insulate my closet with something to help? if so, what?
also, i dont have the ducting run yet so will that make it louder or quieter?

any help is very appreciated!

speedster fan controller 25-30bucks . muffler. insulate it.

get the insulated ducting from the hardware store, that will help. you could build a room inside the room and/or coat the walls in sound board, also purchased at hardware store. or you could use soundboard to build fan boxes, then insulate the box with dampening material. i've also seen fan mufflers at the store. i've found vibration to be the biggest problem with fan noise, make sure the fan isn't vibrating on it's mount. hanging the fans from thick bungee cords or similiar is good for killing vibration.