"tiny bubbles..."

[TANGOMAN]

My 60g is gettin' a ton of bubbles being dumped into the tank from the sump return pipe. Not constant but every five - ten minutes a big blast is expelled. I have made some changes but it shouldn't cause this I wouldn't think ? Remember my story about the the flood caused by the evil check valve ? Well, I cleaned it. I'm runnin' a Mag 12 from the 10g sump. It seems as if air is being drawn into the lines as it travels to the tank. Like a venturi. No leaks... I'm goona' increase my sump to a 20g...some-day.
The water in the sump is pretty "turbulent" but this was never a problem before and "I don't like it...". After 5 years this starts ?
Anyone experienced problems like this before ? Am I missin' something here ? TIA !