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
ADM LSA SC, GMPP heads, LS9 cam, SP 1 7/8" LTs, Magnaflow 3" cat back, ADM CAI, ADM Tuned, DriveShaft Shop DS, ADM Cooler, 3.45s