hi all
the rattling exhuast on the st170 is a fairly common problem i gather, usually caused ny the heat sheald around the CAT corroding and coming loose.
my st170 had the same problem and when i searched various sites the best way to cure this was to either remove the sheilds all together or secure them with a stainless steel cable tie.
i tried the cable tie method but still the annoying rattle at just under 2000rpm!
i then investgated further and just after the CAT the exhaust goes back up towards the floor pannel of the car. it was here i noticed a joint in the exhaust which was loose, caused by a bolt missing! i replaced the bolt and now i seemed to have solved the problem!
hope this may help someone with same problem!
cheers