I've actually had this happen for many years and it happens quite frequently when my car sits out in the cold (on start up.)

I never had it checked under warranty because there was a good bit of discussion about that topic early on. There didn't seem to be any affect on the braking system. When was the TSB on this released? I previously had not seen a TSB.

If there was/is a major problem with this I would expect a full blown recall and not just a TSB. Because there is no recall I'm assuming there isn't any real safey risk (or GM isn't disclosing a safety risk at this point.)