See these threads:
I told them about this sound when I took mine in for the battery reinforcement also, but didn't mention these threads prior to it. So, they said they couldn't reproduce it and didn't find any issues. It wasn't happening for a few days after, but then it started again and has since. I will tell them about it when I take it in to them next. When that will be, I'm not sure.
C4282 - '12 Silver Ice Metallic / Jet Black Leather Interior / Light Titanium Accents
10/15/2011 (6000) Vehicle delivered to customer.