I have this vibration on my car recently also. Started suddenly. I have aftermarket wheels but they were fine for a while. Sudden start to the vibration just a few days ago. Had the wheels rebalanced. Did nothing. I'm about to trade this POS in on a 5.0 and never look back. I've always been a Chevy guy but we are getting crapped on and getting no support from GM or the dealerships that are supposed to do the work.
2011 2SS Black/Black
GPI SS3 VVT cam, GPI intake, Stanless Power 1 7/8" LTs with cats, MagnaFlow X pipe, Borla S Type, VMAX TB, Vararam Tune CAI, PowerBond 25% UDP, Yank SS 3600, Posi Mod, DriveShaft Shop aluminum DS, ADM Cooler, 3.45s, Spohn Trailing Arms, Spohn Toe Arms, Rhino Tuned, TSW Nurburgrings(street), Race Star Bigs/Littles 17"/18", Angel Eyes