The only time I've ever used the primer was the 1st time I set my XP3 up. Even after disconnect and maintenance I just hook it all back up let it sit for a few minutes and it fills up on its own.
Ice beat me to it
. I'm the same, the quick connects keeps the water in the system and gravity pushes all the air out after maintenance.
However, I found the same thing from time to time. It doesn't take much air to make that noise, and sometimes just waiting won't do the trick.
Try this. After you're done with maintainance, lock down the quick release and start like normal. Let it run for about 10 seconds, then unplug it, and lift up the quick release lever (but don't take the hoses off). Lift up a corner of the filter and let it drop, effectively "tapping" any extra bubbles out of the filter. Lock down the quick release and start it up.
If you do this a few times and still have a problem you may have a faulty seal.