I'm sorry if this has been a topic before, I couldn't find it. How do you know if the VANOS is starting to fail or need to be replaced? When sitting in gear at a light or stop sign I can hear a rattle noise coming from the engine compartment. When it began it did it when the motor was cold and once it warmed up it went away. Now it does it most of the time.

2005 E53 3.0l 127k miles