It could be bad, but the chances of cold weather causing it is slim. If you have no loss of performance, then I would try a couple things. First, take a rubber mallot and tap on the exhaust system. There could be a loose heat shield or the inside of the catylatic converter may have come loose and is ratteling. If that does nothing, remove the serp belt and start the engine to see if the sound is gone. (NOTE: WITH THE SERP BELT OFF, THE ENGINE CAN OVERHEAT, SO ONLY RUN IT A FEW SECONDS). If the sound is gone then, one of the belt driven accessories is reacting to the temps.
Let me know what you find, but the timing chain is toward the end of the list. When they get loose and make noise, it usually is a slow process. It doesn't happen all at once and isn't affected by temp.
Thursday, January 14th, 2010 AT 8:08 PM