hi. I've had the same problem with my nissan 2.2dci.(2002 50K).rattling noise in cold weather, after a while when the engine gets warm the noise dissapered. I went to dealer to ask about what it could be. they said it's probably the chain but they have to diagnose it first. They booked me in and said if its the chain it will cost me about 1400 pounds. So I decided to go to different garage. They made a quote and said it will cost me 650 pounds to replace it all(2 tensioners 2 chains and pump). So the mechanic told me to live it there through the night so they can have a look in the morning when the engine is cold what it exactly is. Next day he phoned me and said I can pick up my car. When I got to the garage I was surprised. he said it will cost me 50pounds. He also said that it isn't the chain. he said, that he striped the belt that runs the alternator,water pump and compressor then he lubricated pullies and then he put it back together and the noise was gone. he did it in october 2009 and I don't have the problem again( touch the wood). I think I've heard the noise maybe once or twice but only for like 3 sec. just make sure u change your belt every 2-3 years depence on what milage you do. he said it probably is the belt, he mentioned bubbles on the belt.( don't know exactly what it means). But I'm happy as long as it works. sorry for my english.