Whistling Noise Identification

[DoctorDave005]

I have been the owner of a 2002 Explorer Sport Trac 4wd for several years now. I am looking for help identifying a noise that the vehicle has made ever since I bought it. While running there is a constant high pitch whistling noise. The best I can describe it is like a dog whistle but within the human hearing range. The vehicle makes this noise while idling and driving and it does not change in frequency or sound level. It only becomes less noticeable when driving because the sounds of driving mask it. Most recently I did notice that when parked, if I press the brake pedal the sounds does change pitch some. I am not sure if this is some kind of vacuum leak or how to find the source. This is one of the last things left for me to fix on the truck and it drives me crazy. Any help identifying the source of this noise would be much appreciated.

 

[Gmctyphoon]

Definitely sounds like a vacuum leak.

Look at all the lines, some are hard plastic and can crack pretty easy. After looking everything over real good spray some brake cleaner on suspected areas wit the engine running. A vacuum leak will show if there is one.

 

[94Eddie]

You can use a tube with one end placed to your ear and the other in various parts of the engine bay to isolate where sounds are coming from. This works great for finding valve train noises, injector ticking, etc. Just be careful around moving parts.