Re: duct air turbulence noise
I have a detailed discussion of vent pipes for hoods on my blog.
The same applies for any air vent pipe installation.
Your choice of flex duct pipe is always wrong.
I can't think of any installation where it would perform better than galvanized sheet metal ductwork.
And there are some, vent hood and dryer, where flex can pose a fire hazard.
You should replace it with galvanized sheet metal, tape the seams and strap every section down.
Then pack fiberglass insulation around the ductwork to dampen vibration.
I think you'll be much happier with the results.
Peggy Deras, CKD, CID