Check your tires, wheels and balance. I know it sounds trivial, but it makes a huge difference on cars like ours. I have worked on some older VW's that were so critical that the steering wheel would shimmy at 45mph unless the alignment, etc was 100% perfect.
The problem you describe also sounds like a bad rear axle. The part where you say "noticed it last weekend when we took a sweeping right from a stop sign and went up a good grade of a street". I experience the exact same problem if I accelerate HARD while going up a corkscrew type turn. Where I live is very windy country roads with 2,000 foot elevation changes......It really puts the car through its paces and will do a very bad/violent shake/wobble from the rear end if I really get on it under the right conditions. It is so minute that I haven't gotten around to rebuilding/replacing the axles. I was able solve a more minor but constant vibration by repacking the front axles, changing all fluids and having new tires installed (balance and alignment too).
Last edited by Bobby330xi; 07-06-2012 at 08:20 PM.