is it in the front, or the rear? Worse during acceleration, deceleration, or constant? When occurring, does it continue or stop if you kick it into neutral? Are you sure the wheels are balanced 100%? Has it always been there, or did it just come about- if so, what did you change recently? If the wheel bearing is bad and you know this- replace it first, then reassess the situation.
Did you see the size of that chicken?! -Dirty Steve