My 99 ex did that recently, around 75,000 miles, we thought it was the cv joints going bad, because my car would shake HORRIBLY at freeway speeds, and it got progressivly worse very very fast, overnight. Cv joints dont go bad that fast, so if its been getting worse very fast recently, i found out it was my lug nuts that were loose, and that my wheel was about to fucking drop off on the highway, seriously, i know it sounds stupid, but check it. Its a way quicker fix than a ball joint, lol.