Published · Updated · By the MVHR Expert engineering team
What the sound tells you
- Humming or droning: fan imbalance, dirty impeller or vibration through the mounting
- Whistling or hissing: air forced through a valve opening that is too small or set too high
- Rattling: loose panel, duct clip or flexible duct knocking against structure
- Grinding or squealing: bearing wear — stop using the unit and call an engineer
- Loud only on boost: normal to a degree, but a sign of resistance in the system if very loud
What to try first
- Check the filters — blocked filters make fans labour.
- Make sure the cover is fitted correctly.
- Check that nothing is touching the unit or its ductwork.
- Try a lower boost setting.
- If the noise persists, book a diagnosis.
What an engineer will check
Fan condition and balance, mounting and anti-vibration fixings, duct routes and attenuators, valve settings, filter condition and overall airflow. Many noise problems are solved by cleaning the fans and rebalancing the system.