hi. I have an audi a3 1.6 se petrol 55 plate. I have recently noticed that the exhaust is very loud when the engine is cold.Sounds like the exhaust is blowing. i have had the exhaust checked out @ 3 different garages and all told me the exhuast is fine. I even serviced the car but the problem is still there. The noise only goes away when the engine gets warm. is it anything to do with the cat?