Air in my water line

I am getting lots of air in my water holding tank and water line.  It will start bubbling out of the water outlet of the tank and make the pumps upstream cavitate.  It would also stop bubbling after a while.  I believe I have narrowed it down to one bay. I bypassed all the solenoids and replaced the bypass hose. I am still having a problem. The system is being fed by a pvc pipe and then hoses for each bay running off of it. The only thing I can think of is maybe the check valve in the bay is the problem. 

I also busted open a pump and noticed that everything looked fine.  I then connected three or four pumps to city pressure and they all worked fine.

Autocareforum Update:

I was reading the post: Posts in Subject: New pumps pulsating
He seemed to be having a similar problem. But my holding tank has always had clean water.

But what I learned was I should check the:
1)Tank filter: (sbartlett) I did not really check this. If this is it I will feel really stupid.
2)Check with city water: (MEP1) I believe I checked and everything was okay. But I will check again tomorrow. I tested three or four with city pressure today.
3)Check valve in the bay: (mac) I was thinking this was my problem but now I will know how to check the idea before I just replace it.
4)Weep system: (ghloncc) I have check valves on each bay for my weep, but one could be bad.