[Blacdout96]

I haven't seen a set of HC tires, but if they aren't to be installed in a specific way ( inner/outer) or directional) I think they ment to flip the tires on the rim. It's possible their suspension may be a tad bit too soft, causing excessinve jounce/rebound, creating a cupping effect on the edge of the tread, giving you that slight vibration and why the new tires fixed it for a little bit. I'd have them roadforce matched, and physically inspected for abnormal patterns on the edges. Also, should get a lash check on the rear, did the tech get specs from their techline? (GM's techline can be hit/miss, they either throw a hail marry or you get a guy who was there when they developed the car and knows every nut and bolt)