I've noticed a slight tapping or Clicking sound coming from the engine. at first it sounded mostly like a belt with a warp in it or like a shred tapping as it cycled its path. belt is OK though. I think it's a valve tap but not sure. can hear it on the driver side better. it doesn't get louder if you increase rpms. it gets drowned out by the engine when I increase rpms also but I think the 'tap' gets quicker with rpms. exhaust is clean.