I beg to differ. We have had the vibration at idle in several brand new XTS's we've rented long term for travel over the years all with +/- 10-20 miles on the odo, and we just had another rental XTS with 14k and 0 vibration (no doubt as a rental the cheapest gas was used). Now we have another 19 XTS with 9k which has the vibration. As I posted above I believe it's the cooling fans not being properly balanced or perhaps the assembly not secured properly by the rubber grommets which are there to reduce any vibration the high speed fans cause (which can be significant if not balanced properly), or the fans may be out of synchronization with each other.The vibration issue is almost certainly due to a carbon buildup on the intake valves, which all direct injection engines are known for. It's a common well documented problem. Using a Top Tier gas will do nothing to remedy the problem either, as the fuel is injected directly into the cylinders, bypassing the valves, as opposed to a port injected engine, where the fuel is sprayed across the valves, thus cleaning them. Adding a fuel cleaner additive to the gas tank will do nothing either. There are several easy methods to clean the valves yourself, using SeaFoam, etc. I've done it on my XTS and it works fine.