My MVHR is proving to be a little noisier than I would like, so it is my intention to fit a silencer / attenuator to the supply ductwork between the MVHR unit and manifold.  So far so good.  Price wise, around £50 seems to buy me a ready made unit:   https://www.bpcventilation.com/attenuator-silencer   The silencing material in this case is mineral wool enclosed by a woven mesh material to prevent wool fibres entering the air supply.   The alternative is a homemade