I have a 2002 F-150 V-8 and I'm getting a strange whislte in the engine bay.
I've tried to track it down but it eludes me.
As I'm driving, when I step on the gas it quiet dows slightly and when I let up on the gas that's when it gets louder. By louder I mean just a constant whistle.
It seems to be more noticeable when the weather is cold.
In the summer it would go away after a few miles. No that it's cold, it seems to last longer.
Anyone ever have this noise?

 

While it is whistling, disconnect the IAC and see if the whistle stops.

 

Pdqford,
What is the IAC?
I did notice after a drive of about 10-15 miles the noise went away.
I performed a code reader check and no codes were present.
Like I said before, it seems to only happen when it’s cold outside.
After the engine warms up it seems to go away.
I’m stumped.

 

Sounds like exhaust gaskets leaking. See if its louder in one of the wheel wells.

 

It’s like a smoke alarm in your house. Hard to find where the noise is coming from.
When I open the hood it’s loud but not screaming loud.
Any chance it could be the serpentine belt?
Seems to be more to the front of the engine.

 

Sorry. IAC is the Idle Air Control.

 

to check the belt, take a spray bottle and squirt a little water on the belt while running and see if the squeak changes or is eliminated........ for alternator and idler bearings, you take a short pipe or LONG screwdriver and touch the housing by the bearing, then rest the other end against your ear and listen for grinding... compare 2-3 bearings until you get the "bad" noise figured out.

 

Thanks to all of you who took time to help me out.
I’ll keep you posted with the result as soon as I figure it out.
Again,thanks!
Murf-150

 

You could also take the belt off and start it. No noise=belt driven component causing it

 

The whistle is likely a vacuum leak.
Under idle and low speed throttle openings, the vacuum is the highest at near 20 inches.
As you open the throttle the vacuum goes down and changes the sound you hear.
Get a Stethoscope at the auto store, remove the probe and hunt for the leak with the handle opening same as a Doctor uses his.
Or use a small piece of hose to your ear.
Be a Marine, improvise.
Good luck.
.

 

So, did you try unplugging the IAC when it is making the noise.
That should take all of 15 seconds to check.

That was the issue on my 2002 Navigator when ever the temp dropped below about 25 degrees F. Sounded like a smoke alarm going off. If you goosed the throttle It might stop or if the temp was above 25-30 degrees no more noise.
As soon as I unplugged the IAC the noise stopped instantly. I think my IAC was
marginal and slightly sluggish at the lower temp and it would rapidly cycle back and forth between more air and less air, but couldn’t react fast enough, thus the cycling and that embarrassing noise.l