I've noticed a bad vibration when I first take off, and have the car under a fair amount of torque. If I go to brake torque the engine, it will vibrate back through the car, even though I'm not moving. The entire rear end has been replaced, new aluminum drive shaft. It's a automatic.
You might be a little surprised, but check your mechanical fan... If it is cracked, it will unleash a terrible fury on your car. Mine was cracked and whenever I romped on it, my whole car would vibrate. Ever since I went to my electrical one, no more vibration
While I was checking the fan, I noticed while the engine was running that the harmonic balancer look like it was wobbling. It feels tight, but while it spinning, it looks like a wheel out of round. Can they come loose, or should I just replace it.