2001 Dodge Intrepid Front End Vibration

I have a slight to medium vibration that I can feel in my steering wheel at speeds of 50-70 (the worst being at about 60mph). I had new Kelly tires installed and balanced 7000 miles ago. My mechanic rotated, re-balanced all the tires and checked out the entire front end and found no problems. The only thing he could not check was the wheel alignment. The tires wear fine and the the car does not drift left or right. The only thing that I did myself was a front brake job with new rotors and pads, but I did have this problem before the brake job. My mechanic and I are both out of ideas. Any help would be appreciated.