I replaced my AC Compressor and ran the van up. After about 3 minutes is starts to whistle, almost like it was a belt squeak. It kinda sounded like it was in sync with the engine speed. Checked all belts, pulleys, idlers, etc. There was no noise coming from any of them. However what I noticed was when I turn the engine off the whistle did not stop, instead it continued for about 1 sec then slowly went away.
So the next thing I did was get it to whistle again and open up the radiator cap, no change, then the oil cap, bang! it stopped. Then the PVC, no change, then the breather from the valve cover to the fuel manifold and it stopped. Then I plugged up the breather on both sides and it stopped. So by removing the manifold out of the picture it stopped, doesn't run as good but at least stopped.
Checked all around the manifold for noise and could not hear a thing. I just cannot locate where it is coming from.

Any ever have this issue?