I just picked up a 2013 SS yesterday... and now I hear the rattle during acceleration. Mine sounds like it comes from in front of the passenger seat by the firewall. I emptied the glove box, but it is still there... Generally in the 1st to 4th gears around 2,000 rpm.
Annoyed to already have to think I will be taking it in for service... my 2012 Camaro 2LT I traded it in never had a single problem. Great way to start my V8 experience.