Yeah the hum is annoying. I still sit my fans on surfaces... one sits on the roof of a flower tent.. two sit on insulation in the attic. one is suspended for convenience.
I wrap my fans in soft material. The ones in the attic are wrapped with old pillows duct taped around them. It looks pretty shitty but no vibrations and it absorbs the wind noise too. The one on the tent is wrapped in duct insulation.
What I'm saying is, ime, insulating the fan sitting on a surface that is not hard works better for the vibration and does more for mechanical and wind noise.
of course, depending on your setup hqnging might be more cinvenient.
even if you do hang though... insulating the fan will help with noise.some people build boxes around the fan and insulate... you czn use blankets, pillows, duct indulstion, whatever.
The large fan turned down though... that is key. I've ran 4,6,8 and 10 in fans in many different ways. Large fan with lower speed is going to do more for the win and mechanical sound than anything;;
Also, usig all insulated ducting makes a difference.