Check that the exhaust system is sound and there are no breaks developing on the joints to the back box etc as this will cause the pipe to become loose and contact the bodywork or heat shielding.
If the exhaust is OK then it could be the heat shielding over the exhaust pipe has come adrift of its fixings and the exhaust is touching it and making it rattle, I would suggest finding the offending piece of heat shield and removing it altogether.
Other rattles could be the Catalytic Convertor heat shield is loose - this is attached to the bottom of the cat and often the welds break that hold it on - pull it off is the simple solution.
Steve J, August 2007
