A question about filters

Hi Guys,

Love the site, it's been a great help so far.

I've just set up my tank, no fish at the moment, just the filter running. The tank's 160L/~40G and I'm running a canister filter. Every now and then the filter will make a bubbling sound, and a few air bubbles will come through into the tank. I'm worried it might be a leak in the filter, letting air into the system, but it could be normal, I don't know. It didn't do it at all for the first few hours of operation last night, but this morning I noticed it. Can someone shed some light.

cheers,

Luke

It's an Atman EF-1.

It's been running about 36hrs. I just tried rocking it slowly and when I tipped it back and a lot of air escaped, and now it's not doing it anymore. Looks like it was just trapped air.

Thanks guys.