Signs & diagnostics
A change in the sound of your extraction - a deeper hum, a new rattle, more vibration - is often the first thing staff notice. Frequently it is grease loading the fan, not the fan simply wearing out.
The short answer
When extraction starts to sound louder - a deeper hum, a new rattle or vibration, a strained note that was not there before - the usual cause is that the fan is working harder to move the same air. As grease builds up on the impeller and inside the housing, the blades get heavier and the free area of the duct narrows, so the fan labours against the restriction. That extra effort is what you hear. A change in the everyday sound of the system is often the earliest cue that grease has taken hold, and it frequently arrives before anything is visible.
Why grease changes the sound
Two things happen as an extract system fouls up. First, grease and carbon collect on the fan's impeller blades, adding weight and throwing the balance off - an unbalanced fan vibrates, and that vibration is both audible and damaging. Second, deposits along the ductwork reduce the space air has to move through, so the fan has to work harder to pull the same volume, running hotter and noisier in the process.
The result is a system that no longer sounds the way it did when it was clean. A smooth, familiar background note gives way to a strained hum, a rattle from a loose or loaded component, or a vibration you can feel through the canopy. Because the change is gradual, staff often adjust to it without registering the cause - which is why a noticeable shift in the sound is worth treating as a diagnostic signal rather than an annoyance.
Reading the sound as a warning
The reason the sound matters is that it tracks airflow. A fan that is straining is a fan moving less air than it should, which means the whole system upstream is capturing and clearing less - smoke lingers, the kitchen feels hotter, and grease clears more slowly, compounding the problem. So the rising note is not just a comfort issue; it is an audible proxy for the loss of extraction performance the grease is causing.
There is a cost to ignoring it. A fan left to labour against a restriction wears its bearings and motor faster, and an unbalanced impeller accelerates that wear. What starts as a change in sound can end as a failed fan and an unplanned closure. Catching it at the noise stage means dealing with grease; leaving it can mean dealing with a replacement.
What to do about it
A noisier system is a prompt to inspect the fan and the duct rather than to turn the extraction up and carry on. Cleaning the impeller and housing rebalances the fan, and clearing the ductwork restores the free area air needs to move through - so the fan runs quietly and efficiently again. Done as part of a full clean, it addresses the cause of the noise, not just the symptom, and heads off the wear that leads to failure.
Questions
Not always - worn bearings, a failing capacitor or a loose fixing can also change the sound. But in a commercial kitchen extract system, grease loading the impeller and narrowing the duct is a very common cause, and it is the one worth ruling out first because it is preventable and points to a wider contamination problem.
Turning it up masks the symptom and makes the wear worse - you are asking an already-strained fan to work harder still. The change in sound is a signal to find and clear the restriction, not to push the fan past it.
A straining fan is moving less air than it should, so the noise tracks a drop in extraction performance. As the fan labours against grease, capture at the cookline weakens, smoke lingers and heat builds - the sound is an audible proxy for that loss of airflow.
Usually, yes. Cleaning the impeller and housing rebalances the fan and clearing the duct restores the free area for airflow, so the system runs at its normal quiet note again. If noise persists after a clean, it points to genuine mechanical wear that needs a separate repair.
A fan left to labour wears its bearings and motor faster, and an unbalanced impeller speeds that up. A change in sound can progress to a failed fan and an unplanned closure - so catching it early keeps it a cleaning job rather than a replacement one.
Phoenix Duct Clean · by the numbers
A change in the sound is worth checking before it becomes a breakdown. We inspect the fan and duct, find the restriction and restore the airflow the system was designed for.