First noticed a minor vibration that could be felt in the steering wheel while attempting to maintain a low speed. Typical when entering a 40 to 45 mph speed limit and trying to maintain posted speed. When I accelerated hard or let my foot off the gas peddle the vibration went away. I took the car in for service and they could not identify the problem. Since then the problem has gotten worse. The car has been in the shop now 4 times and we are still not at the bottom of the problem. The car now vibrates all the time, still most noticeable while trying to maintain a constant speed with slight acceleration. Now this happens at all speeds. I can feel the vibration in the steering wheel, the seat, and on the floor. I noticed when I come to a stop and shift into park the vibration goes away. The car is under warranty and the dealer has been very good about the situation giving me a brand new loaner each time, sometimes for over a week. The dealer believes the problem is in the transmission but can't seem to pin point the problem and claims GM has no directive or recall related to my problem. I am scheduled to take it back for service next week. They will send me out in a new 2012 Impala or Malibu which I can't complain about, however, the issue is frustrating and time consuming. The vibration issue is taking away the enjoyment of driving what other than the problem would be a fine automobile. I highly recommend the dealer, however, not much praise for GM.