ya it's hooked up, it's weird because i actually have 2 maxijets and one shoots out alot of bubbles all the time and the other shoots some out every couple of minutes
i just had this problem and i have no air tubes. i emailed aquarium systems, they make maxi jets, and he told me to turn it upside down in the water and tap on it for a while, since doing this i have hardly anymore bubbles coming out.
I have the exact same powerheads and one of mine was just doing this last week. Hubby took it out, took it apart and cleaned it real well and it never did it again. hope that helps.