I have a 90 420sel that has about 115k on the clock. I have had the timing chain/rails/tensioners replaced about 4k ago. I have noticed in the last little bit that while sitting in a parking place with the car idling it will occasionally knock or peck a single time. What could this be? It will do it a single time and then it will be probably a minute or two before it does it again. Since I have had the timing job done recently, I don't think it could be anything related to that. Can anyone tell me what it might be and is it dangerous as far as a dissaster happening if not fixed?