Car: 93 400SEL (83K miles) When my car's Air Injection Pump is ON at cold start, it makes a "raking metal" sound. It is not loud by any means but it was troubling at first because I originally thought that the sound was coming from the timing chain. The sound eventually goes away after 2 minutes and the engine sounds fine afterwards.

Is the "raking" sound normal for the Air Injection Pump?


thx