I was getting that when I was using the ext 5000 filter , I was pushing my Eheim 2262 filter thru the 10" house filter , the force of the water was pushing the co2 thru the scrub pad and out into the tank. Maybe what you need is something to breakup your flow going in the house filter. Like my post 439, with pic's of my new co2 reactor mine is still running nice and silent and no bubbles in my tank and my reactor stays full with water 24/7.
Thanks for the response! In my original post I said I didn't think it was the CO2, but you're right, it is. After I wrote the post, about an hour later my lights turned off for the evening, as well as my CO2. I noticed I no longer heard the reactor, so I went up to the tank and low and behold... no bubbles. So you filled the reactor with bio balls? What is the suction screen you mentioned?