Do you have a sunroof? If you do check the drain tubes. remove your headliner. You will be able to see where they are attached at the base of the sunroof (on all four sides leading down over the top of your windows) and get a friend to go to the drain points (wheel wells and rear of car) and plug the end with his thumb while you blow air down the tube. Then if you do find a leak make sure you dont have any punctures in your seals and then check for RUST!