I remember now from back when I was looking into the problem...
Some people said they had success by making the holes larger in the spraybar, something about too much back pressure. I don't use the spraybar but I opened the single nozzle larger anyway. That didn't help either.
Also, I believe they said too much media in the baskets will cause it as well. I removed everything but 2 of the foam pads and it still had the bubble problem.
I even emailed the company but never heard from them.
Now, I just put up with it and unplug it when we are going to have company.
Also looking forward to the day when I have enough LR
that I can just toss the hunk-a-junk.