It seems that I always have a very tiny bit of air in the filter. I can turn the bleed valve maybe a 1/8th of a turn and let the air out and it takes a second or two for water to start coming out. And then the next day the air is there again. The filter is making some subtle noise (cavitation?) and it gets a bit better after I let the air out. Nothing significant or excessive, a tiny bit of air and some subtle noise.
Is this normal or do I have a small vacuum leak? Can the water outgas if there is some pressure drop somewhere in the filter? No bubbles in the returns.