Aside from my typical idle studder that I still had checked out to be sure, my other issue has been a wobble while cruising on glass smooth roads--especially at 40 and above--and often the same thing just from a stop as accelerating. This is with the upgraded 18" GY Eagle LS-2 tires.
Described that today at the dealer and let them go at it. Idle, normal. Wobble? There was way too much air in the tires--I did it, and disagree, putting them to 34-35 vs. the squashed looking and soft 30--and balancing one (I believe) of the wheels. I played with the air pressure before to no effect on the wobble just more stiffness in general with higher, but they reset them lower and sent me off after driving it 12 miles themselves.
The first 2 times I drove it a mile or two back to the office and then out to grab something, it did seem smoothed. Then I left for home tonight and accelerated a bit more briskly than usual onto the highway and felt the exact same wobble as before the whole way home, along with more squish because of the lower pressure. Baffled why it seemed to re-appear, but it did--or maybe it never left.
Like a light jiggle I can feel in the seat and car in general, I think from the front. I'm still wondering if it's the tires at all because of the shake while under power, but them balancing and road testing seemed like an answer.
Oh well. Just barely crossed 750 miles
Common as rattles and vibrations may be to the G6, the 2 I drove were perfect, a co-worker's '08 GXP coupe has zero vibes after 5k, and mom's '08 Malibu on the same guts is dead steady and smooth. Drives me nuts but I'm hoping another round may be the answer, as with my sunroof noise.