Thanks guys, sorry for the late update. It was the center bearing on the drive shaft as a couple of you guessed. There was also an issue with one of the brake calipers dragging, new control arm bushings, new radiator/cooling stuff, an oil leak, and some random other things. They changed the oil and did an alignment. It cost about $3,000 but I had them fix every tiny thing wrong with the car. When I got behind the wheel it felt just like when I first drove it! I'm still going to look for a new car but I'm going to take my time and enjoy driving the ZHP for a while longer. So one more back on the road!