98 Escort zx2 "whistle"

Now I know this sounds kinda odd but my 98 escort zx2 whistles and I really would like to know why! (its quite annoying to have a whistling car)

This is what I know:
1. The whistle only occurs when the engine is hot (ie temp gauge is in the middle)
2. The whistle sounds like a steam whisle (ya know like old steam trains had)
3. The whisle only occurs when the the engine is loaded (ie when its in gear, not when idling, in neutral, or with the clutch in regardless of rpms) and only while accelerating mildly or maintaing speed, not when slowing down or under heavy acceleration the only exception to this is after driving for a time when the car is shut off, just after the engine stops moving it will whistle once more
4. The whistle is louder outside the car then in
5. The whistle doesnt appear to be dependant on stearing position, rpms, or speed.
6. I am not crazy, other people hear it to!

Some Suggestions Ive been given:
1. Belt -> just replaced this two days ago, by the way this has been happening for a while but seems to be getting worse (or at least now that I notice it its REALLY annoying)
2. Pulleys -> This could be it except the pulleys really shouldn't keep rotating after then engine is stopped where as the whistle sometimes occurs just after the engine is stopped

Any ideas? im really stumped on this one! please someone help be for I do go crazy (or simply say f*** it and sell the car hehe)

Jon Estey

it is your 3rd vacum hose on the plenum

Thanks for the info!

sorry for being a dumb newb but where is that?

Jon Estey

if you look at the intake hose, near where it meets into the engine you will see a metal disc with 5 tiny rubber hoses in it take a close look at them on will have a hole in it. thats your whistle