Every car on the road has an exhaust pipe spring that allows the exhaust system to have a certain amount of flex. As the car is moving over bumps in the road, these vibrations move through the entire car, including the exhaust system. To stop the exhaust system breaking at its welded joints, the exhaust pipe spring is utilized to absorb the movement in the exhaust system. Without this spring the exhaust system would degrade very quickly and it would need to be replaced or repaired much more often than necessary.
Exhaust pipe springs are usually fitted between the components of the exhaust, such as the silencer box and the piping, to allow flexing between the components. Without the spring, which is held in place by a bolt running through its centre connecting the two parts, the constant bending backwards and forwards of the metal would cause the exhaust to break. This is why this spring was introduced in cars to alleviate this breakage.
Most vehicles employ the use of an exhaust pipe spring to maintain the integrity of the exhaust system as a damaged exhaust system that does not work efficiently will mean the car can lose power, and also that the harmful emissions are often not being funneled through the catalytic converter and are thus harming the environment. Make sure that your car exhaust system is secured by an exhaust pipe spring and you will be assured that your exhaust will last a long time. When you hear a knocking coming from the exhaust system it might mean that you require a new exhaust pipe spring. Alternatively, ask your mechanic to check if you need an exhaust pipe spring when the car is in for its annual service.