Rattling usually points to an impeller, debris or a loose component; gurgling often means trapped air; loud splashing is commonly a low water level; and humming can be vibration against glass or furniture. Unplug the filter before opening moving parts, clean the impeller and intake, re-prime canisters or HOBs as required and make sure the unit sits level and secure.
A filter that suddenly becomes noisy is often telling you something has changed in the water path or moving parts.
Rattling and grinding
Grit, snails, plant fragments or worn impeller parts can make a motor rattle. Disconnect power and inspect the impeller chamber according to the manual.
Do not run a pump dry while testing it.
Gurgling and trapped air
Canisters commonly become noisy after maintenance if air remains inside. HOB filters may also suck air when the intake is not fully submerged or the water level is low.
Re-prime the system and check hose connections for air leaks.
Waterfall noise
A HOB return becomes louder as the tank water level drops. Topping up or raising the water level within the safe range shortens the drop and reduces splashing.
A baffle can also soften the return if compatible with the filter.
Vibration and resonance
A quiet motor can sound loud when its vibration transfers into a cabinet, lid or glass panel. Reposition the unit, tighten loose parts and use manufacturer-approved rubber feet or padding where appropriate.
Noise after flow loss
A blocked intake or clogged media can make a pump strain or cavitate. Clean mechanical stages and confirm normal flow before assuming the motor is failing.
Frequently asked questions
Why is my filter noisy after cleaning?
Trapped air, an incorrectly seated impeller or a misplaced media basket are common causes.
Can a noisy filter damage fish?
The noise itself is usually less important than the underlying fault, but severe vibration or loss of flow should be corrected.
When should I replace the impeller?
If cleaning and correct seating do not stop rattling and the impeller or shaft is visibly worn or damaged, replacement may be appropriate.
Sources and further reading
This guide separates general aquarium arithmetic from fish-welfare decisions. For species-specific limits, always check the needs of the fish you intend to keep.