Canister Filter Problem

Guys, I am been driving out of my mind here at the moment. My canister filter, keeps on making this, what I can describe as a popping noise every 1 min and then it releases air from the tank, it's driving me insane. I literally have tried everything to solve the problem that I can think of. I put new seals on it, tried different intakes on the filter/s but nothing changes this gas is constantly stuck in the tank. It's like the o2 or co2 is been separated inside the tank

I even went as so far as to buy a new canister filter and then the new canister started the same noise. It's like a popping type noise then air comes out of the system only a few bubbles, but I cannot find the cause of it. I am running an external heater along side it and then a co2 diffuser inline.

Yesterday I put the old canister filter back on again and the noise stopped only for it to return again today. Really is a total mystery I can't get my head around it. I am thinking, that it's something to do with the co2 so I have turned it off for the moment, but I know it will take some time before the levels pass out.

It's really driving me mad, I am the type of person who likes to just set something up and leave it running apart from maintenance, but I am at it every hour to try get it too stop making the blooming noise... The filter is the All Pond Solutions EF1000+ and the newer filter is the JBL e1501