Noisy Canister Filter (Fluval FX4)

[kkirkt]

I have a Fluval FX4 on my 125 gallon brackish tank. It makes a "vibrating" sound. Fixes??

More details:
I have a "media bag" over the inlet to keep fry out of the filter (found 7 live fry at one of my filter cleanings). I do notice reduced flow if I don't clean the bag about every 2 weeks (I usually clean it with weekly water changes, but I'm understocked and I get lazy occasionally).
The noise went away (completely) when I throttled the FX4 outlet valve about 1/2 way, but I'd rather not live with the reduced flow.
The noise has gone away at least once (and come back), after a water change.
If I lift the canister up, I still hear it, but it's not as loud (most of the noise comes from the vibrations being transferred to the aquarium stand the canister sits in).


I don't think it's the impeller, since the noise goes completely away when I throttle the outlet valve 1/3-1/2 [but I went ahead and ordered a replacement impeller to have as a spare, anyway]

It's really not that loud, but it is definitely louder than the FX4 used to be. I can live with it, but I'm concerned the vibrations could damage something eventually. I assume it's just something vibrating in the canister but I haven't taken it apart yet (I already admitted that I'm lazy, right?).

I'm really hoping one of you can magically fix it through the internet without my doing anything, but I'm guessing I'll have to just clean my filter earlier than I was hoping to. [And of course, since it won't be running, I'll probably never truly know what was vibrating]

Dreaming of having a sump . . . . .

Thanks
kevin

 

[TheWolfman]

I recently had a noise in my fx5 and took apart the impeller and found 2 small pebbles jammed inside the impeller, it’s worth a look. You should also make sure there’s no slack in the lines as it can cause air to build up inside the canister witch can also cause the filter to be noisy.

 

[duanes]

Even 1 grain of sand or snail can cause an impeller to become knocked slightly off axis, and this may cause cavitation. Which sometimes sounds like crackling, or grinding. Although the link below focus's on large pro pumps, it can happen to any centrifugal pump large or small.
Understanding and avoiding pump cavitation - Flow Controlhttps://www.flowcontrolnetwork.com/understanding-avoiding-pump-cavitation/

 

[Jexnell]

Let's go another route. Have you checked the bottom of the filter if the rubber feet are still there. When looked at normally it looks as if it sits on the three feet. But if you feel under each foot has some rubber isolation pads to prevent noise transfer. Maybe they got knocked off during a recent move of the filter.

 

[kkirkt]

While I understand how a small item can cause a problem with the impeller, I don't understand why the sound would go away when I throttle the outlet (hence, I don't think it's the impeller). But I will check that.

 

[TwoHedWlf]

While I understand how a small item can cause a problem with the impeller, I don't understand why the sound would go away when I throttle the outlet (hence, I don't think it's the impeller). But I will check that.

That makes me think it's due to intake restriction, maybe cavitation? Make sure the filter's clean, no restriction of the intake strainer, pipes are clean, etc.

 

[kkirkt]

Update:

I took off the filter media bag (from around my filter intake- used to protect fry) to see if the sound was reduced. It wasn't (so I replaced it). I throttled the output (~1/2 closed) to stop the noise until I had time to really fix it. I also turned on my air pump to get more surface agitation due to the lower filter output (usually I don't keep the air on).

I finally had time to clean my filter last week. There was noticeable mulm in the filter (which I partially rinsed off in old aquarium water). I did not have time to even look at the impeller. When I restarted the filter (with no throttle) there was practically no noise (just the low volume, normal, hum). The loudest piece of equipment now is the air pump, which I'll probably turn off.

I'll try to pay attention to if the noise comes back and how long it takes (to come back).

Thanks to those who offered advice or suggestions (twohedwlf, jexnell, duanes, TheWolfman,