if it is a vacuum leak you can use brake cleaner and spray it around the vacuum lines (KEEP AWAY FROM SENSORS & ELECTRIC!) and when you here the engine idle droop (almost as if it was about to stall) then you have likely found your vacuum leak.

That's the easy way to test for vacuum leaks at least, specially if you don't have access to a smoke tester.

 

I tested the vacuum lines, no leak. Checked all intake track and installed the open cone type filter. All is tight. Suspecting pullys now. Bought a stethascope for this part.

 

I have the same problem. mine is a low whistle and only happens when light throttle is applied. It started after i cleanded throttle body and used seafoam treatment in the vacuum line. i installed all new gaskets and checked for vacuum leaks as well as cai connections no leaks found.

 

is it worse when its cold and does it get louder when giving it more gas?? transmission seal. mine has been doing it for a year after i switched the transmission i damaged the pump seal on installation.

 

Mine whistles too....when my girl friend gets in the truck and honestly I don't blame it!

 

Is it worse at cold start up? Check for broken exhaust manifold bolts. This is a common problem and makes a whistling noise, especially under acceleration.

 

That would suck but I've heard that's common on the 4.7 anyways

 

Not sure if its a coincidence or not but i had my magnaflo y pipe installed around the same time and i noticed the 3" outlet has a spot that didn't get welded. Its actually leaking condensation upon startup. Its either that or when they installed it they broke an exhaust manifold bolt and i just haven't seen it yet.

 

pictures or it didn't happen....


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Most common sources for these types of noises are the following:

PCV Valves (most common in my personal experience)
Vacuum Lines
Pulleys/Belts (Check Belts & Tension)
Intake Filter
Transmission (Change Fluid if hasn't been done in awhile)
Rear Diff. (Change Fluid if hasn't been done in awhile)
Exhaust Leak (Super hard to detect leaks that small till they get worse)
Intake Manifold Gasket (not very common)
Throttle Body & Intake Connectors (much more common in older silicon/cheapo connection joints)


I have come across an easy method for detection if it is along the intake tract. Get yourself a few cans of Brake Cleaner Spray (Rattle Can type), then spray in short bursts along the intake tract, stop and listen between sprays... when you here the idle droop (almost like its going to stall) you have found the area your intake/vacuum leak is.

NOTE: DO NOT SPRAY ANY SENSORS OR ELECTRICAL CONNECTORS!!!!

Disclaimer: Do this at your own risk, I assume no responsibility if you damage any part of your vehicle.

I personally have never had a problem when doing this myself on my own vehicles, and it has always helped me find the leaks.

 

I had to go there last year. Right side rear snapped off. Could happen again though. Its def. not the same sound as I had when that problem exhisted. I gotta get under there to listen. I will check back in when I come up with something.