What would you check if there is a strong vibration inside the cabin?
I can feel the strong uniform high-frequency vibration from front row seats and steering wheel at idle.
It immediately goes away when I press the gas pedal.
I can see that the plastic bag next to me is shaking.
No check lights, runs great at high speed, strong enough power.
Parking, Reverse, Drive: strong vibration
Neutral: little less vibration but still strong.
2012 LR4 100k miles

I am thinking about motor mount as a reason.

 

Does it remain in neutral or park? What RPM at idle? Could be mounts or a number of other things. I have a long thread related to idle issues which cause shuddering and vibrations.