i am the new owner of a 93 mx-6 ls and im having a problem. on the highway, once i get up to 55/60, the steering wheel starts shaking like a bastard. i figured it to be a tire balance/alignment problem, but ive taken it in twice to have all four tires balanced and the front end aligned, yet the problem still persists. also, when i turn the wheel hard to the right and accelerate slowly, i hear a strange thump sound. i was wondering if first, these two problems are related, and second, if has anything to do with the after market wheel(15 inch) and tires the other owner put on. thanks for the help.