I have an 06 ss/sc. I have about 10000 mile son my car now, but ever since I got the car reverse always grinds the first time I go to use it, but is fine after that. For example, when I leave work and put it in reverse, it will grind, but once I put it in Neutral and then back into reverse again it is fine. It does it everytime. You think the synchro's are going? Anybody else have this problem?

 

I have this problem on my old truck. Probably the syncros. But your car is most likely warrantied. Take advantage of it. Best of luck to you.