I'm getting the whistling sound in my 04 GC 4.0. It only whistles at idle speed (let off the accelerator while driving). it goes away when i press the gas pedal. It is definitely an air leak around the intake area.

I have found posts on this, but they all seem to end with no fix.

Has anyone ever actually fixed this problem? The truck runs fine, it's just annoying as hell.

 

Bringing this back from the dead. I'm still getting this noise. It only seems to happen when the outside temperature drops below 60 degrees. Being that it is now winter, it has come back.

If anyone has figured this out, please help. When I let the truck idle to diagnose it, it goes away. Kind of hard to figure out when it only happens while driving.

 

New belt? Maybe the alternator? Stick your ear in there and see were it comes from.

 

its most likley a air box noise or intake tube if it has baffles in it try swaping it with another air box and intake tube and see if it goes away im a tech at a chevy dealer and i see this from time to time

 

wouldn't have thought of that

 

Simple, down and dirty! You can eliminate an intake vacuum leak with a propane torch. DON'T LIGHT IT!!! Just bleed gas and play it around the manifold area. If there is a leak, the engine will respond to the propane by speeding up. A technition would want to do a smoke test, which works, but can be expensive. A whistling sound to me indicates a vacuum leak especially under high manifold vacuum such as deceleration. Today's cam timing doesn't pull much vacuum at idle, so it is difficult to find a leak. Propane enrichment works well!

 

Try idler pully.

 

or a bottle of brake cleen or starter fluid will work too

 

+1 on possible vac leak, should be easy to find with a can of brake/carb cleaner.

Try cleaning the throttle body/plate, also clean the IAC passage and valve. If one was dirty it could create turbulence or stick at a abnormal position.

If you have a cold air or open element air filter it could be normal.

 

starter fluid works excellent but can lead to an uncontrolled fire

 

That's why I like propane! If it flashes, it's gone in a split second!