Shaking at high speeds 2003 Aerio

I own a 2003 Suzuki Aerio. When I drive on the highway at above 55 miles per hour I hear a slight thumping noise and the car shakes. When I go above 69 mph, I can no longer hear the noise. When I take my hands of the wheel the car doesn't seem to drift. My tires have worn down fairly quickly in the last year. I have replaced the tires twice. Any suggestions?

Jen :(