Well, as I said, keep an eye out for this issue. My dealer today REFUSED to replace my exaust system again even though I am still under warranty. According to them, GM will not allow them to replace the part "because there is nothing wrong with it." They said that as my exhuast system "settles in" that this is a natural progression of it and that "there is no fix." Okey Dokey...since when does a car company design a car to intentionally develop an obnoxious whistle that does go away when the new part is installed. hmmmm
Now some day, I was told, if GM ever decides that this really is a problem, I'm on the list for a replacement. Sadly, with Pontiac as now the sacrificed group, I'm thinking that GM isn't going to put much effort into Pontiac issues.
I was given the number of GM's customer service to file a complaint and now am awaiting a verdict.
As for the black soot, I was again told that this is a non-issue and that my fuel is running just fine and dandy.