Hi,
Before you all despair with thoughts of "not again", i wonder if anyone has any ideas.
We have started using our new Zehnder MVHR in our passive house and we have been surprised how noisy it is. he other issue is the levels of CO2 which i thought would be lower.
We paid for a design service and commissioning but we fitted it ourselves. Many days were spent carefully ensuring all bends were swept, runs kept short, ducts not touching potential problems areas and carefully following all the guidance.
The supply plenum and valves in the bedroom and lounge are the worst culprits although we can hear them all. The people commissioning have had 2 goes at it and it is disappointingly noisy. We are having to set it to turn down low before bedtime then increase later at night to allow us to go asleep. The problem then is the CO2 builds up over 1000.
Anybody had any similar issues.

The plenums do generate noise. It seems reasonable given the volume and swirling of the air in them. I hope you have them isolated somewhere? The valves shouldn't generate much noise.

Our plenums are slightly noisy. They are mounted above the ceiling in our guest bedroom. The ceiling is 15 mm plasterboard and skim on resilient bars and I fitted some extra Tecsound membrane to reduce noise further.

The CO2 in our bedroom goes up to nearly 800 when we're both in there.

Part numbers or photos may help identify them. Air volumes etc would also be useful. Are the parts plastic or metal?