I have a 2007 Malibu 4 cyl/Auto (bought new in late 2007) and have had it at dealers three times for a vibration that always occurs at 15 mph. This started at 2400 miles. They try to either say they can't feel it or it's "normal" for this drivetrain. No engine light appears. I've rented this vehicle (2005 and 2006 model years) with plenty of miles multiple times and no problem. In fact, one dealer checked other models on the lot and only the 2007 model exhibits this problem. The only difference that they know of is the engine mounts...