External filters are designed to run quietly. If yours is making an unusual noise — such as rattling, buzzing, humming or gurgling — there’s usually a simple reason. Most issues are caused by either a damaged impeller or air trapped in the system. Follow the guide below to identify and fix the problem.
1. Check for a Damaged Impeller (the spinning part inside the motor)
A damaged or unbalanced impeller is one of the most common causes of loud noises. It may rattle, vibrate, or make a grinding sound when the filter is running.
What to do:
Switch off the filter at the mains and unplug it.
Remove the motor head from the canister.
Locate and remove the impeller (refer to your manual if unsure where it is).
Inspect it carefully for:
Cracks or breaks
Debris or limescale build-up
Separation between the magnetic body and the plastic propeller
Missing or worn rubber grommets at either end of the impeller shaft
If the impeller shows signs of damage, it should be replaced.
Need help checking the impeller? There is a visual guide on the instruction manual which would be inside your box. If you need a copy go to the product listing and click on Product Instruction to locate the user manual.
Need a replacement?
You can order spare impellers here.
2. Check for Air Trapped in the System
If you hear a gurgling, bubbling, or humming sound — especially when the filter is first started — air is likely trapped inside the system. This is common if the filter hasn’t been properly primed or if there’s a small air leak in the intake line.
How to remove trapped air:
Turn off the filter and unplug it.
Check all hoses and connections:
Ensure the intake and outlet pipes are fully submerged in the aquarium.
Confirm that all connections are tight and sealed.
Fill the canister with aquarium water as high as possible before restarting.
Prime the filter:
Press the priming button firmly and repeatedly.
You should see air bubbles rising inside the tank and the hoses filling with water.
Continue until water flows smoothly through the pipes without bubbles.
Once the air has been cleared, the filter should run almost silently.
Not sure how to prime the unit?
Click here for detailed priming instructions.
Still Hearing Noise?
If you’ve:
Checked and/or replaced the impeller
Removed all air from the system
Ensured all parts are correctly fitted and submerged and the noise continues, please contact our support team. We’ll be happy to help you diagnose the issue further.