Gentlemen, your collective knowledge and experience would be appreciated on a problem which occurred yesterday. Driving home after visiting my other car which is having an engine rebuild coincidentally, car running OK, parked and got changed to take the family out for dinner. Started the engine and, although at idling normal speed, the noise was frightening and vibration to shake your fillings out. I can only describe the noise like one of the pistons is hitting the head. The vibration is like only one side of the engine is firing. I have seen on another post about the flywheel and the vibration feels more like an engine imbalance than anything else. There is no excessive smoking from the exhaust and, as I said previously, engine idle speed is normal. I will be getting the car towed to the nearest independant with VAG-COM for full diagnostic and would appreciate your input so I can assess what my options will be. A4 2.5 V6 TDi Quattro Sport saloon. First registered as a demonstrator April 2002 by Vincents, now Shrewsbury Audi, fitted with Superchips 200bhp by the dealer from new. I am the only other registered keeper and this wonderful car has now done 165,000 miles. New Turbo fitted at 125k. K&N induction kit fitted soon after that. Regular servicing at either Vag-Tec or Inde-Tech. New cam belts fitted by Inde-Tech at 149k.