Rhythmic 'whoosh-whoosh' noise and vibration at the indoor unit – from dirt?
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Drumul Taberei, Sergent Nuțu Ion street, 1976 block, 9,000 BTU Midea, 5 years old, bedroom. For about a month, at high speed, there is a rhythmic whooshing and the housing vibrates slightly. At low speed it is fine. No metallic knocking. I read it could be the roller unbalanced by dirt. Is that it or is it the bearing?
What is really happening
The cross-flow roller is a long cylinder with dozens of thin blades, factory-balanced to the gram. When dust-and-biofilm felt builds on the blades – never evenly, more where condensate splashes – the mass distributes asymmetrically and at high speed a cyclic centrifugal force appears: rhythmic whooshing (loaded blades 'cut' the air differently) and housing vibration. Lower the speed, lower the force, symptom gone – exactly what you observe. A worn bearing would give a squeal or a continuous rumble, at low speed too. Split studies show the roller is the most fungus-laden component; imbalance is the mechanical effect of the same layer that also causes smell. Prolonged, untreated vibration can indeed wear the bearing over time – so cleaning is mechanical prevention too.
- The casing and fasteners.
- Vibration transmitted to brackets or the wall.
- The fan and possible deposits or abnormal contact.
- The blower (cross-flow fan) is the most fungus-contaminated component of a split unit, more than the filter or the front of the evaporator. [Indoor Air, 2023]
- A typical evaporator fouls enough to double its pressure drop in about 7.5 years, reducing airflow by 5–7% and raising fan power by 1–10%. [Lawrence Berkeley National Laboratory / , 2002]
- Washing with alkaline detergent, brushing and high-pressure rinsing reduces fungi inside the unit by more than 99%. [Indoor Air, 2023]
What we do on site
- We listen to the unit at all speeds beforehand, as a baseline.
- Collection cover; cleaning solution on the roller (inside and out) and evaporator.
- Pressure wash in place, roller fully rotated, blade by blade, until evenly clean.
- Pan and hose; sanitising solution.
- Outdoor unit, washed in place.
- Test at maximum speed, 10 minutes – if the whooshing is gone, it was the dirt. See current rates on the Prices page.
What you can do yourself
- Until we come, low speed or 'Auto'.
- Filters every two weeks – less dust on the roller.
- 'Fan' before shut-off – a dry roller does not 'glue' dust.
What NOT to do
- Do not push anything through the grille to 'clean' the roller – you break the blades and unbalance it for good.
- Do not overtighten the housing screws to stop the vibration.
- Do not lubricate the bearing with an online spray.
Prevention
Annual sanitising keeps the roller balanced and quiet. Noise that grows with speed is your signal that it is time.
When to call us
0764 012 943, Monday–Saturday 08:00–20:00. Drumul Taberei.
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The information on this page is educational and based on cited sources; it does not replace medical advice. We do not do repairs, installation or refrigerant circuit work.