Hello , My 1996 Galaxy has a similar problem on the driver side . The 'jacking' explanation is clear non-sense . If you look underneath the chassis it soon becomes clear that it is simply impossible - because of the huge box sections of the chassis . I think that the bulging is due to rusting between the box section of the chassis and the sheet metal floor . The rust expand the metal etc... I don't think it is particularly serious - given the substantial size of the chassis box section - but then I could be completely wrong :-)