Last weekend our S90 was parked in the driveway. As we drove up in our Miata, which gives you an excellent bumper eye view, my wife thought that the Volvo looked like it was sitting lower on the passenger side. My first thought was that this was an illusion because the driveway has a pitch to drain the water away from the house, but to satisfy her I got a tape measure and measured from the ground to the back bumper, and the passenger side was indeed sitting 3/4" lower than the drivers side. Thinking there might be an inconsistency in the concrete of the driveway, I put the car in the garage and measured again. Still 3/4" lower.

What might cause this? Is this worth looking into, or is it a don't care?