By Hektor Jorgo
A Penguin BioWheel that's been running quietly for months and suddenly starts rattling, grinding, or clicking can be alarming — especially since the filter usually keeps running normally despite the noise. The good news is that the most common causes are simple, cheap, and don't involve the filter actually failing.
Short Answer
New or sudden noise from a Penguin BioWheel filter is most often low water level (causing the impeller to run dry), debris caught in the impeller well, mineral buildup making the bio-wheel click, or — especially right after cleaning — an impeller that wasn't fully reseated. Genuine impeller wear is also possible, but it's a gradual process and should be near the bottom of your checklist, not the first assumption. Working through water level, then the bio-wheel vs. impeller distinction, then debris and reassembly, resolves the large majority of cases without any parts needing replacement.
Check Water Level First
This is the single most common cause of a sudden noise increase, and it's the fastest to check and fix. As water evaporates between top-offs, the water level drops — and if it drops far enough relative to the filter's intake, the impeller can end up running partially dry or drawing in air, which produces a loud grinding, whining, or rattling sound that's distinctly different from the filter's normal quiet hum.
Top off the tank to its usual level and listen again. If the noise disappears (or drops dramatically) once the water level is restored, this was the cause — and it's worth keeping an eye on evaporation rate going forward, especially in drier seasons or with open-top tanks.
Bio-Wheel Clicking vs. Impeller Noise
If topping off the water doesn't resolve it, the next step is figuring out which moving part is making the noise — the bio-wheel and the impeller produce noticeably different sounds:
- Impeller noise is typically a continuous grinding, buzzing, or rattling sound, coming from the impeller housing where the pump mechanism sits.
- Bio-wheel noise is typically a rhythmic clicking or ticking, once per rotation of the wheel — often caused by mineral deposits building up on the wheel's axle or bearing surface (common if the wheel has been exposed to air and allowed to dry, even partially), or by the wheel sitting slightly misaligned and lightly contacting its housing as it spins.
Many BioWheel designs let you temporarily lift out or stop the bio-wheel without shutting off the filter — if doing this stops the clicking but the underlying hum continues, the bio-wheel (not the impeller) is the source, and a gentle cleaning of the wheel's axle and housing (rinsed in old tank water, not scrubbed aggressively, to avoid stripping the bacteria living on it) is usually enough to quiet it down.
Debris in the Impeller Well
Small debris — a piece of gravel, a snail shell fragment, plant matter — can get drawn into the impeller well and cause a rattling or buzzing noise as it interferes with the impeller's rotation. This is more likely if the filter's intake doesn't have a strainer, or if the strainer has a damaged or missing section.
Removing the impeller assembly and checking the well for anything that doesn't belong is a quick check — and if you find debris here repeatedly, it's worth checking your intake strainer, similar to the intake-blockage checks covered in our guide to Penn Plax Cascade canister filter problems for a different filter design with the same underlying issue.
After Cleaning: Impeller Reassembly
If the noise started right after you cleaned the filter, the most likely cause is that the impeller assembly — the impeller, its shaft, and the rubber bushing/cap that holds it in place — wasn't fully or correctly reseated when you put it back together. A slightly misaligned or angled impeller can spin with a noticeable rattle or buzz even with nothing actually damaged.
The fix: remove the impeller assembly again, confirm all of its parts (impeller, shaft, rubber grommet/cap) are present and in good condition, and reseat it carefully — the impeller should spin freely with light finger pressure before you close everything back up.
When the Impeller Has Actually Worn Out
If you've checked water level, distinguished bio-wheel from impeller noise, ruled out debris, and confirmed correct reassembly, and the noise persists (or has been gradually increasing over months, rather than appearing suddenly), genuine impeller wear becomes the likely cause. Look for visibly chipped or worn impeller blades, or a shaft that wobbles more than it should when spun by hand.
The fix here is a replacement impeller assembly — these are sold separately for Penguin/BioWheel filters at low cost, and replacing just this part restores normal operation without needing to replace the housing, motor, or bio-wheel.
If you're weighing a full filter replacement instead of a parts-level fix — for example, because the tank has outgrown the filter rather than because of this noise issue specifically — our AquaClear 110 vs. Emperor 400 comparison covers how the Emperor's bio-wheel design (the same general technology discussed here) stacks up against AquaClear's sponge-based approach for larger tanks.
Quick Reference
- Top off the tank's water level first — this resolves the most common cause of sudden filter noise
- Distinguish continuous grinding/buzzing (impeller) from rhythmic clicking once per rotation (bio-wheel)
- Check the impeller well for trapped debris (gravel, shell fragments, plant matter)
- If noise started right after cleaning, recheck that the impeller assembly is fully and correctly reseated
- Bio-wheel clicking is often mineral buildup on the axle — a gentle rinse in old tank water often fixes it
- Gradual, slowly worsening noise over months points toward impeller wear — an inexpensive replacement part, not a new filter
