I have a 05 lease, S AWD. Recently when standing at a light or something, or after shutting off the engine I began hearing periodic "clungs". Very similar to the ones you hear when the engine is normally cooling down but louder. It sounds like it may be coming from the muffler, but I'm not certain. These clunks are typically 20 seconds apart. They tend to stop after a few minutes after turning off the engine. Should I be worried? These are definately louder then the cooling down noises I'm used to hearing... although this is my first cold weather with the MO.