2005 Silverado 5.3L Automatic

When I do a hard acceleration from slow speeds, I hear a whistling sound in the engine. It sounds like some sort of vaccuum leak. Dealership can't recreate it and every time I'm there I can't either. Yet, two miles down the road I hear it again.

My wife calls it the "automatic horn" because we only really hear it when I'm passing someone going 20 in a 40 mph zone or when pulling into our driveway (which is up a small hill after a hard right turn).

Anyone experience this before? Any ideas?
Thanks.

 

Here is an excerpt from a GM STB:

"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."

 

Thanks for the info. I guess the automatic horn is a feature, not a bug...