Even from the factory, the weight of the fiesta ST's standard exhaust system causes issues to the stock ford bushes that allow a lot of movement which can lead to the system knocking. This issue becomes even worse when fitting bigger aftermarket systems where the exhaust can be known to hit the valance.
To solve this exact issue on our own demo car we tried a number of different bushes and whilst testing various systems for companies found these to allow minimal movement whilst not resulting in excessive vibrations in the cabin.
Come in a pack of three. Genuine Ford product