The only thing the filter intake is near is the intake to the uv sterilizer I run in this tank. There are no airbubbles in the intake hose, the only bubbles you can see are where the water coming in and being pushed down to the bottom is, in other words you can see the flow into the bottom part of the cannister, then the bubbles form, burp their way up to the top between the side of the cannister and the media containers and exit via the outlet pipe. The only thing I can think of is that the surface the filter is sitting on may not be completely even.