I just replaced a left bearing on my 96 Zetec, which corrected the following symptoms.
1 Sounds like car is riding on bad or bare tires, with a slight vibration and sometimes a "hardly noticeable" thumping sound when cornering.
I did the same thing you did as far as alignment, tires checked and rotated twice, and balanced. You problem sounds like it could be a wheel baring, wouldnt hurt to replace at $39 each plus labor. See this link and good luck.....
http://www.contour.org/cgi-ubb/ultimatebb.cgi?ubb=get_topic&f=3&t=003894
