Check your tires. How old are they? I had the same problem, had the brakes checked and replaced and it was still there. I was going to do alignment, but there seems to be no symptoms for this. I asked two mechanics and they checked and said to replace my tires. I was hesitant because the tires looked fine, but they were the stock tires (1996). So, I changed them even though it's against my own opinion. Guess what? The mechanics were right. 
1996 GL Red Contour, Zetec, ATX
K&N Filtercharger,aluminum mesh grill
OBX Fog Lamps, Viper alarm
FocusSport High Performance 8mm Spark Plug Wire, LEVOC custom ATX shifter
Panasonic CQ-FX620U Head Unit, Panasonic CX-DP88 8-disk changer, Infinity Kappa 572.5 Front/Rear
JCWhitney 80W Xenon Headlight low beams
CEG sticker, Bridgestone Potenza RE950
Magnaflow SS Race Series#14830 & Resonator #10424
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