using a short length of dryer ducting; if the inlet is long enough with a few bends, the hum is completely missing. with the same on the outlet, you can plumb it right to an external vent. I was able to run an S7 in an RV I lived in; for over a year. Never heard it; Just kept an eye on it.
You can get PVC coated exhaust hoses pretty cheap and they muffle noise and insulate heat a lot better than just aluminum alone.
An example of what i use.
https://www.amazon.com/gp/product/B0791TKB51/