I have a similar feeling. TC off is normal, but with TC on and a wet road, if I accelerate and it turns on it chops/pulses really harshly, and everything bounces in the cup holders. In the snow, not at all. I felt similar rattling in the cabin once when I ran through a pothole at night that cracked the sidewall on my tire.
I'm not sure if it's normal, I know it's obnoxious and sounds harmful on a wet surface, and it'd probably scare the crap out of any passengers I have if it activates.