Fitted new exhaust mounts at tail pipes and centre, the exhaust and heat shield are all tight but when starting and reversing the exhaust bangs off the underside of the car. When starting the car I can see the front of the exhaust shaking quite a bit. I have checked the cat spring bolts and they are tight so was thinking could it be engine mounts? The exhaust is standard and the car has low miles, only ever does it when starting or reversing!