Hi, I have an astra mk4 1.8 16v sport. I have recently noticed a a slight knocking from the engine when driving. The knocking seems to go away when the engine is disconnected from the gearbox, I.e the cluch depressed, leading me to believe that it may be a gearbox fault? The noise is present in every gear selection and seems to be more noticable as the rpm increases. Any ideas?