There was a loud knocking noise coming from the engine when I started the car (R129)this afternoon. The car has been sitting for a week and a half in the garage, and the noise sounded like my gasoline car turned into a diesel. It only lasted for about the time it took to warm up (one minute or less)and it sounded loud at first and gradually faded away. Is it something I need to be concerned with? Is there anything to do with the car been sitting and it needed time for the oil to circulate in the engine? During the whole episode, the oil pressure was at 3, engine idle fine, and no smoke coming out from the exhaust. The outside temp was around 40F. It also ran fine when I drove it down the road. Anyone can shed some light for me will be appreciated.