Whats causing this noise? on 2003 Ford F-150 Lightning

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
My 2003 lightning has a high pitch whistling noise(sounds like a tea kettle) coming from behind the supercharger a little to the right. It only does it idling or when im at a steady speed but when I accelerate it stops. What could this be?
(2) Answers
(6) Comments
pcv elbow may have a vacuum leak causing this. common issue with these motors.

Thanks and if not replaced soon could it cause more of a problem?
it will throw a code eventually. i would get it confirmed asap.

where exactly is the pcv valve. is there a website i can go to?
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It is on the passenger side valve cover. There should be a sticker with a diagram under the hood.
It was the elbow thanks but when I took the hose off the intake I noticed just a little oil, was the elbow causing that or is it something else
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That is normal due to wear in the pcv valve just replace the valve
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It sounds like a boost or vacuum leak