most likely the tracking, may also be a worn wishbone, quite a common wear item on these
rust? there has been a few issues with rust of late, it may be worth checking underneath to see the extent of the problem. While most of the car was galvanized, the floor was not and we are now getting to the stage where the problems are starting to show. Typically the problem has been along the sills and around the rear edge of the rear floor panel where the drain holes are. An ordinary wood chisel does a great job of removing the underseal, often the underseal looks good put its no longer stuck to the metal, its only when its peeled off can the true extent can be seen. The good news it responds well to a coating of Hammerite if caught in time and the floor is not too difficult to work on if some welding is needed.