Trying to track down an issue with my pcm not communicating and noticed something odd with the alternator. I have the truck on but it doesn't run right now, while I'm testing wires and pins etc. while on, but not running the alternator makes a high pitch ring sound. Continuous no fluctuation or tone change, and barely in our hearing range. Quite annoying. lol. Why does it do this? Worked fine when it was running and no noise running. Its always done this, never knew why, but I'm grasping at straws trying to find whats messing with my pcm.