Judging by what I read, it looks like a combination of different tires (snow tires have different rubber compound than summer or all seasons), 40 psi in the tires which can give you a little bit stiffer ride than the recommended 36 psi, and my final opinion is the tires may be mounted on the wheels to where the high spot in the tire may need to be moved to receive a smoother ride. You can ask the shop to see if they "Road Forced" the tires when they balanced them. Road forcing simulates driving conditions and helps insure the best possible balance of the tires. If the road force is higher than what is recommended for a smooth ride then the machine will instruct the operator to spin the tire on the wheel to move its high spot. I hope this makes sense and is of help
