Whistle sound from X5 3.0i engine

I have a 2006 X5 3.0i and love it. Wondering what the whistle sound is that comes from the engine when I press down on the gas. It is only audible when I press down slightly, as if to maintain the speed I am going. If I press down further, to go faster, it goes away. Thoughts???!!!

Normal noise is what you're hearing from the intake manifold. Don't be worried.

Here's a possible reason/solution (new post)

http://www.xoutpost.com/bmw-sav-foru...tml#post925551

EenyBear, you are comparing an X-5 that has a different drivetrain completely. The X-5 you are refering to has a new generation engine, not the M54 engine in the 2006 E53 model. A whistle from the intake manifold upon acceleration is quite normal in the M54.