I talked to my service manager last week. If this is the same noise that I have (more of a loud rubbing noise, particularly when just starting, say backing out of a parking spot) then it is likely an issue that GM is currently working on. It affects Tahoes and Suburbans, too, as they use the same steering box. According to my SM, GM is not replacing these yet. I'm hanging tight on this for now. There are other thread on this subject, too. Some describe it as a loud "howling" or worse. My NON-MECHANIC opinion is that these descriptions are all pointing to the same steering box issue.
Mine makes a tick over small bumps, too. Kinda feels loose. This is the problem that GM is addressing by greasing the steering shaft as mentioned by someone above. I think there is a TSB for that.