I seem to have noisy fuel injectors. When the engine runs, there is a low clacketty-clak. I first thought it was the valves, but I put a rag over the injectors and that deadened the sound. It does not matter if the engine is cold or warm, or how many kms have been driven, the clicking is there. It has been like this since I bought the car, and does not seem to affect performance or idle. Any ideas??