Air suspension.

I have a discovery TD5. The suspension is constantly going down on the right hand side. Even on short journeys i have to inflate the back air bags in the suspension. When sat in the vehicle and it is not running you can feel the car bang a couple of times or vibrate as it deflates. This problem only ever occurs when the car is stood stationary and not moving.

Check the bag for a leak with soapy water, look for the air bubbles coming out of it.