My maxi-jet sometimes pumps out air

[shine~on]

I've had a maxijet 900 in my tank for a couple weeks now and for some reason every once in a while it will pump out a burst of air bubbles. Not really that much, but enough to leave bubbles floating around in a certain area of my tank
I tried tapping on it to see if more air would come out, but it didn't work. Any advice on how to fix this or what's going on?

 

[1911_guy]

Do you have the venturi plug installed? Or the tube?
Is the powerhead completely submersed?
Air has to be fed into the maxi-jet for air to come out unless it is taking it from the water somehow.
If you have the tube installed instead of the plug make sure it is completely closed or air will enter the jet stream.

 

[shine~on]

No, that's what's weird it is completely submerged. I am pretty sure there is no tube or valve installed. I've used this one before without these issues.