Signs & diagnostics
A fan that has picked up a rattle, a hum or a new vibration is not just getting old - it is reporting a change in how it runs. Grease on the impeller and rising resistance in the duct both alter the load on the motor, and the sound is the early warning most kitchens miss.
The short answer
A fan that has picked up a rattle, a hum or a new vibration is not just getting old - it is reporting a change in how it runs. Grease on the impeller and rising resistance in the duct both alter the load on the motor, and the sound is the early warning most kitchens miss.
The detail
An extractor fan runs against the resistance of the whole system - duct length, bends, filters and the discharge point. When that resistance is steady, the fan settles into a consistent note. When grease builds and resistance climbs, the operating point shifts and the sound changes with it.
The most direct cause is grease on the impeller itself. Even a thin, uneven coating unbalances the wheel, and an unbalanced wheel vibrates. That vibration is what you hear as a hum or rattle, and it is also what accelerates bearing wear and stresses the motor shaft over time.
Rising duct resistance adds to it. As filters and ductwork load up, the motor works harder and runs hotter under sustained load, especially through a long service. A motor that is undersized or already grease-fouled struggles first, and a strained motor is a noisier motor.
So a louder fan usually means one of two things, often both: the impeller is carrying grease and out of balance, and the system it is pulling against is more restricted than it was designed to be. Neither is a reason to turn the speed up - that only spends more energy against the same problem.
What it means for you
Noise is the cheapest fault to fix because it is the first to appear. Caught early, the cure is usually a clean - the impeller is degreased and balanced, the duct resistance comes back down, and the fan returns to its proper note and operating temperature. Left alone, vibration wears bearings until the motor needs replacing.
A clean also settles the question of what you are hearing. If the noise clears once the system is back to TR19 Grease condition, it was contamination. If it persists, the bearings or motor may already be worn, and you have caught it before a failure mid-service.
Phoenix Duct Clean degreases the fan and full system, restores the airflow it was built to move, and flags any mechanical wear found during access - so a change in sound becomes a planned clean rather than an unplanned breakdown.
The service behind the guide
Sibling guides
Smells even with extraction on · Grease on the canopy lip · Hotel extraction across outlets
Questions
Not immediately, but it is an early warning worth acting on. Vibration from a grease-loaded impeller accelerates bearing wear, and a strained motor runs hot. Catching it at the noise stage usually means a clean fixes it, rather than a mid-service failure and a motor replacement.
No. Turning the speed up spends more energy against the same resistance and does nothing about grease on the impeller. It can make vibration and heat worse. The fix is to remove the grease and restore the airflow, not to force more power through a loaded system.
An even, balanced impeller spins quietly. A grease coating is never even, so it unbalances the wheel and sets up vibration, which you hear as hum or rattle. That same imbalance stresses the bearings and shaft, so the noise is also a wear warning.
If the noise is from grease and resistance, yes - degreasing and rebalancing the fan and clearing the duct brings back the original note. If it persists after a verified clean, the bearings or motor are likely worn and need mechanical attention, which the clean will have flagged.
As part of the whole-system interval - three months for heavy use, six for moderate, twelve for light, adjusted by a cleanliness risk assessment. The fan loads last but matters most mechanically, so it should never be left out of a clean.
Phoenix Duct Clean · by the numbers
A new noise is worth acting on early. Book a clean and inspection before it becomes a repair.