Sound

Hi all,
So I am curious, I have a 6" inline fan pulling 440CFM through a cooltube in a 36"x20"x63" tent. However this much air movement is totally
superfluous in such a small space (23.4cubic feet). So right now if my fan is on high it changes the air in there 18.8x a minute lol.
Currently it is connected to a speed controller that drops it to 40% power. Insulated Rubbermaid box trick,insulated ducts, but sound is still semi noticeable.
I see my options as follows, change to a 4"fan with 6" ducting, 4" fan with 4" ducting to 6"cool tube, 6" fan with 4" ducting.
Which option would best reduce sound? Btw sound is mainly motor hum.

what brand/model inline? is it the fan itself or the air movement causing the noise?

The fan is just a no name one from growtents.com , they sell shitty shit btw. As previously said sound is mainly motor hum.