I took my car into Arnold Sharks in St. Helens to get a faulty coolant sensor fixed and what I thought was a lose heat sheild put right. When I got the car back they said they needed to order some parts and to call back today. So I called them this morning and they told me they have ordered a new centre box and sleeve to fix the rattle. Am I right in thinking that a centre box is on the exhaust and I will be presented with a bill if I let them go ahead and fit it and not done under warranty? Also what is a sleeve? The car has got to back anyway because it sounds like a brake disc is sticking. There is a loud whining sound coming from the back left when driving along. They said they checked them and all seems fine. They even said the brake discs were less than 50% worn so it might not be the brakes. Any other suggestions what it might be?