I have a 2012 Camaro and after running it a couple of weeks now have a noise under the back end. Took it to the garage, they say this is normal but I don't think so. It sounds like something is hitting. Anyone else having a problem with noise under the car?

 

I have a 2010 and when backing up and giving alittle gas it makes a weird noise and when sitting inside it sounds like it is coming underneath the console area. its weird noise like a metal noise.