Since it is a sports car, it has stiffer suspension. It is possible for the shock to leak fluid and gas out. This happened on my 95 MR2 last summer. Both of my rear shock were shot and rode lower than usual. Although I never put anything heavy in the trunk, my mech told me since the shock is stiffer, it senses more road vibration and takes more toll on big bumps and hole. Didnt cost much but was replaced free under warranty. I would think you have the same problem I did unless something major happend to the car before?