When I rev the engine in neutral gear everything sounds ok. smooth and " quiet". when I drive the car and put the power on the engine sounds " throaty and rough" as though the exhaust is leaking. The exhaust has no leaks and is fairly new. I did remove the " Cat " and put in extra pipework to fill the gap. Do not need a cat in the UK for 92 vehicles. Once the vehicle is cruising everything is silent. Its Only during hard acceleration that the noise occurs.