Lube:

How long had the car been sitting? If it was for a few days, there may have been flat spots on your tires. I drive my car maybe once per week. When I get onto the freeway I'll notice vibration like my tires need balancing, but I know it's the flat spots. Once the tire temp increases the vibration goes away. Might this be what's happening with your car?

Just a thought.

Brian