Taking the humming noise out of a building?

I have had this issue for quite some time now, and as I start adding to the room, i.e equipment, and small changes that may need to be made in the future. if I decide to change it up, this is a 10x12x12 building I put on my property. I currently have two 6 inch fans and one 8 inch that are mounted with pad to keep the vibration from going directly in the wall. But I still hear a good amount of noise from the outside. I don't have it insulated or anything, but it's a sealed building. Any ideas on how I can keep the noise just in the building, so Its muted from the outside?

Thanks!

Try hanging the fans with rope hangers

Are they in contact with the wall..Try and suspend with bungess to absorb vibration

make fan boxes Thu reduces the sound and carbon filter silencer for the ducting thus will reduce and use sound deadening mats ie egg boxes on the inside walls or acoustic matting works