I have a 2500HD GMC Sierra 6.0l gas. I have experienced a "whistle" that I think is coming from the transmission. It occurs under steady throtle conditions, i.e. steady speed, I have had the dealer look into it, but they said it was normal. Anybody else experience this?? Is this normal??

I have expierenced such a whistle. Different then the normal turbo noise. I have not had it looked at nor has it appeared to cause any problems. (Other than hurting my ears)

Greg

Could be an exhaust note, does it change with engine RPM? Vehicle speed?

An exhaust note? Not familar with that. I am not sure that it changes with speed, but it does change at a constant speed. It may come and go with the cruise on.

This could be your noise. I have heard of blocking off that IAC passage using epoxy but I doubt GM would allow that under warranty. If it's not done perfectly the epoxy could get sucked into the engine.

Whistle Noise from the Throttle Body Area on Light Throttle Acceleration - kw idle intake manifold off accelerate GMT305 GMT360 GMT370 GMT800 GMT805 GMT806 GMT820 GMT830 #PIP3086A - (Jan 6, 2005)

Whistle Noise from the Throttle Body Area on Light Throttle Acceleration
The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.
Condition/Concern: (http://service.gm.com/servlets/BlobShtml?ShtmlFile=1580607&psdid=437&evc=sm#ss2-1580607)
Some of the vehicles listed may exhibit a whistle noise from the throttle body area during light acceleration if they are equipped with a GEN III engine and an electronic throttle body.
Recommendation/Instructions: (http://service.gm.com/servlets/BlobShtml?ShtmlFile=1580607&psdid=437&evc=sm#ss3-1580607)
This is a normal noise characteristic that could be experienced on these vehicles if they have an electronic throttle body. The same intake manifold design is used whether the engine has an electronic throttle body or a mechanical throttle body. Due to this, electronic throttle body engines still have an IAC passage in the intake manifold. The whistle noise may be the result of an airflow disturbance that can occur as incoming air contacts the unused IAC passage.

This could be your noise. I have heard of blocking off that IAC passage using epoxy but I doubt GM would allow that under warranty. If it's not done perfectly the epoxy could get sucked into the engine.

Whistle Noise from the Throttle Body Area on Light Throttle Acceleration - kw idle intake manifold off accelerate GMT305 GMT360 GMT370 GMT800 GMT805 GMT806 GMT820 GMT830 #PIP3086A - (Jan 6, 2005)

Whistle Noise from the Throttle Body Area on Light Throttle Acceleration
The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.
Condition/Concern: (http://service.gm.com/servlets/BlobShtml?ShtmlFile=1580607&psdid=437&evc=sm#ss2-1580607)
Some of the vehicles listed may exhibit a whistle noise from the throttle body area during light acceleration if they are equipped with a GEN III engine and an electronic throttle body.
Recommendation/Instructions: (http://service.gm.com/servlets/BlobShtml?ShtmlFile=1580607&psdid=437&evc=sm#ss3-1580607)
This is a normal noise characteristic that could be experienced on these vehicles if they have an electronic throttle body. The same intake manifold design is used whether the engine has an electronic throttle body or a mechanical throttle body. Due to this, electronic throttle body engines still have an IAC passage in the intake manifold. The whistle noise may be the result of an airflow disturbance that can occur as incoming air contacts the unused IAC passage.
Where is this passage located??? Do you have a diagram/photo that can give me an idea of what it looks like and where??