Chocovision machine tempering question

I recently purchased a Chocovision Revolution Delta (I've been working with a Chocovision X3210 for over a year now) and have used it twice so far. Both times, I've tempered milk chocolate and it has produced an unusual number of tiny bubbles by the time it's tempered. Any idea why this might be happening and what I might have to do to fix it? I've seen this very rarely (but I have seen it) on my X3210 but seems like the Delta is doing it everytime (ok - twice...).

Any thoughts on what I might be doing wrong?

Thanks much,

Geetha