[lil drummer boy]

Ok I've got this problem which so far really doesn't seem like a huge problem, but I'm afraid it might be a warning sign that could build into something major. The winter here has been cold. It's about 30-35 degrees average during the day, and it gets down in the teens and twenties overnight. Every morning after a cold night when I leave for work I notice a bump in the rear end of the car. It almost feels like I'm driving with a flat tire. It's really noticeable at first, then I'll go down the road a mile or so and stop at the stop sign at the end of the street. Once I take off again the bumping is gone. It only does this when it's really cold and mostly overnight when the temperatures hit their lowest, and only for the first mile or so down the road then it's gone. Has anyone else had this problem? Might anyone have any idea what it could be? Is it something to be worried about?

I appreciate any feedback... thanks!