Llama

The aquarium system is brand new, just filled it up today and leaving it to work. There isn't any fish or anything inside, and the filter is a EHEIM Classic (2213) cannister filter.

Either way, its AMAZINGLY quiet almost all of the time, just at very rare intervals it starts making strange 'fizzing' noises, as if having problems passing water through it or something, it continues making these for less than a minute, then continues as usual. I believe I saw some bubbles escape from the pressure side of the pipe, but I don't know where air could have come in or anything... if there's a hole in the tubing I'd assume I'd know by now.

Anyone can tell me what the fizzing noise is? It continues working even while it does it...

Llama

Hmm, I think I've localised the problem, its bubbles of air...

Where are they coming from though? Anyone has any ideas?

Dozey

I’d suggest that you make sure all your hose connections and gaskets are in good condition and tight. Another possibility might be from the intake picking up air bubbles from a bubble wand or air stone if you have one.

Llama

Right, been meaning to update this. The bubble sounds stopped after day 1, haven't heard any more since. Don't have an air stone, the bubbles the filter out gives is at the surface, while the filter in is below it.

I checked the hose connections, everything was (and is) fine. I'd assume I would have flooded my room otherwise.

It just stopped on its own. Rather strange.