Just to let others know, My 2010 Vibe had a brief rattle sound lasting about one second when starting with a cold engine . It sounded like the heat shield over the catalytic converter was rattling, but that wasn't it. The dealer could not hear this til I left it , overnight, & started it the next morning. I had printed out a copy of the TSB linked below, & took it with me. They heard the noise , called GM advisors, & did the repairs. They said that it was the first time they had seen this problem. There is even a short video on youtube about it. If you have this problem, it may pay you to make a copy of this pdf file when taking it to the shop. The warranty covered everything & they gave me a rental for 2 days.
http://www.empirepao.com/tsb/T-SB-0087-09.pdf