Lanse I bet that the vibration is the grinding wheels. Some of the wheels are too hard and they will hold up better but they suck at cutting smooth.
If you have a wheel dressing stick try shaping the wheel. IF you do not, then can use a concrete block. Take the grinder and grind on the block to shape/smooth/open up the wheel.
Remember that trick if you have to grind aluminum or some other material that will plug the grinding wheel. I have just used a rough piece of concrete. Quartz rocks will work too.