First of all, I love driving my stock '02, 1.8t. It's so sweet when it's right. At about 80 mph, I notice how the road inevitably, dips and rises because, with every rise that normally causes cars to squat a little, a vibration occurs until the suspension is finished responding and the car is planed out again. When the road dips, no vibration, but I know, with every dip, there is a rise and the same vibration. When this downward stress is present, this vibration happens. The car has about 230,000 miles on it. I like this car enough to try to find out what's going on and address it. It's better than a car payment every month and this car is sweet! I can do many parts changes, even on these shits, but need diagnostic help. Any ideas would be appreciated.