Originally Posted by Ragin'Cajun

I have an 02, with polished stock wheels that have not been curbed either and my left rear developed a crack about 3 months ago. The dealers were very suspect of it at first, and even tryed to say it could have happened mounting the tires if I had done so at an "unapproved location" -- gave me a bunch of bull. But in the end they replaced the wheel on GM's bill. Mine looked just like what you are describing and it is a crack in the wheel itself, get this fixed ASAP.

There are others who have had this problem also, see if you can search for the topic.